Make more uids nullable (#5794)

Content.Client/Body/UI/BodyScannerBoundUserInterface.cs

@@ -14,9 +14,6 @@ namespace Content.Client.Body.UI
         [ViewVariables]
         private BodyScannerDisplay? _display;
 
-        [ViewVariables]
-        private EntityUid _entity;
-
         public BodyScannerBoundUserInterface(ClientUserInterfaceComponent owner, object uiKey) : base(owner, uiKey) { }
 
         protected override void Open()
@@ -43,7 +40,7 @@ namespace Content.Client.Body.UI
                 throw new ArgumentException($"Received an invalid entity with id {scannerState.Uid} for body scanner with id {Owner.Owner} at {entMan.GetComponent<TransformComponent>(Owner.Owner).MapPosition}");
             }
 
-            _display?.UpdateDisplay(_entity);
+            _display?.UpdateDisplay(scannerState.Uid);
         }
 
         protected override void Dispose(bool disposing)

Content.Client/Body/UI/BodyScannerDisplay.cs

@@ -13,7 +13,7 @@ namespace Content.Client.Body.UI
 {
     public sealed class BodyScannerDisplay : SS14Window
     {
-        private EntityUid _currentEntity;
+        private EntityUid? _currentEntity;
         private SharedBodyPartComponent? _currentBodyPart;
 
         public BodyScannerDisplay(BodyScannerBoundUserInterface owner)
@@ -104,9 +104,6 @@ namespace Content.Client.Body.UI
 
         public void UpdateDisplay(EntityUid entity)
         {
-            if(entity == null)
-                return;
-
             _currentEntity = entity;
             BodyPartList.Clear();
 
@@ -125,12 +122,7 @@ namespace Content.Client.Body.UI
 
         public void BodyPartOnItemSelected(ItemListSelectedEventArgs args)
         {
-            if (_currentEntity == null)
+            if (IoCManager.Resolve<IEntityManager>().TryGetComponent<SharedBodyComponent>(_currentEntity, out var body))
-                return;
-
-            var body = IoCManager.Resolve<IEntityManager>().GetComponentOrNull<SharedBodyComponent>(_currentEntity);
-
-            if (body == null)
             {
                 return;
             }

Content.Client/ContextMenu/UI/EntityMenuElement.cs

@@ -15,7 +15,7 @@ namespace Content.Client.ContextMenu.UI
         /// <summary>
         ///     The entity that can be accessed by interacting with this element.
         /// </summary>
-        public EntityUid Entity;
+        public EntityUid? Entity;
 
         /// <summary>
         ///     How many entities are accessible through this element's sub-menus.
@@ -28,7 +28,7 @@ namespace Content.Client.ContextMenu.UI
         public readonly Label CountLabel;
         public readonly SpriteView EntityIcon = new() { OverrideDirection = Direction.South};
 
-        public EntityMenuElement(EntityUid entity = default)
+        public EntityMenuElement(EntityUid? entity = null)
         {
             IoCManager.InjectDependencies(this);
 
@@ -40,7 +40,7 @@ namespace Content.Client.ContextMenu.UI
             LayoutContainer.SetGrowVertical(CountLabel, LayoutContainer.GrowDirection.Begin);
 
             Entity = entity;
-            if (Entity != default)
+            if (Entity != null)
             {
                 Count = 1;
                 CountLabel.Visible = false;
@@ -51,7 +51,7 @@ namespace Content.Client.ContextMenu.UI
         protected override void Dispose(bool disposing)
         {
             base.Dispose(disposing);
-            Entity = default;
+            Entity = null;
             Count = 0;
         }
 
@@ -59,23 +59,25 @@ namespace Content.Client.ContextMenu.UI
         ///     Update the icon and text of this element based on the given entity or this element's own entity if none
         ///     is provided.
         /// </summary>
-        public void UpdateEntity(EntityUid entity = default)
+        public void UpdateEntity(EntityUid? entity = null)
         {
-            if (Entity != default && _entityManager.EntityExists(Entity) && !entity.Valid)
+            entity ??= Entity;
-                entity = Entity;
 
-            if (entity == default)
+            // check whether entity is null, invalid, or has been deleted.
+            // _entityManager.Deleted() implicitly checks all of these.
+            if (_entityManager.Deleted(entity))
             {
                 Text = string.Empty;
+                EntityIcon.Sprite = null;
                 return;
             }
 
             EntityIcon.Sprite = _entityManager.GetComponentOrNull<ISpriteComponent>(entity);
 
             if (UserInterfaceManager.DebugMonitors.Visible)
-                Text = $"{_entityManager.GetComponent<MetaDataComponent>(entity!).EntityName} ({entity})";
+                Text = _entityManager.ToPrettyString(entity.Value);
             else
-                Text = _entityManager.GetComponent<MetaDataComponent>(entity!).EntityName;
+                Text = _entityManager.GetComponent<MetaDataComponent>(entity.Value).EntityName;
         }
     }
 }

Content.Client/ContextMenu/UI/EntityMenuPresenter.cs

@@ -101,18 +101,16 @@ namespace Content.Client.ContextMenu.UI
 
             // get an entity associated with this element
             var entity = entityElement.Entity;
-            if (!entity.Valid)
+            entity ??= GetFirstEntityOrNull(element.SubMenu);
-            {
-                entity = GetFirstEntityOrNull(element.SubMenu);
-            }
 
-            if (!entity.Valid)
+            // Deleted() automatically checks for null & existence.
+            if (_entityManager.Deleted(entity))
                 return;
 
             // open verb menu?
             if (args.Function == ContentKeyFunctions.OpenContextMenu)
             {
-                _verbSystem.VerbMenu.OpenVerbMenu(entity);
+                _verbSystem.VerbMenu.OpenVerbMenu(entity.Value);
                 args.Handle();
                 return;
             }
@@ -120,7 +118,7 @@ namespace Content.Client.ContextMenu.UI
             // do examination?
             if (args.Function == ContentKeyFunctions.ExamineEntity)
             {
-                _systemManager.GetEntitySystem<ExamineSystem>().DoExamine(entity);
+                _systemManager.GetEntitySystem<ExamineSystem>().DoExamine(entity.Value);
                 args.Handle();
                 return;
             }
@@ -139,7 +137,7 @@ namespace Content.Client.ContextMenu.UI
                 var funcId = _inputManager.NetworkBindMap.KeyFunctionID(func);
 
                 var message = new FullInputCmdMessage(_gameTiming.CurTick, _gameTiming.TickFraction, funcId,
-                    BoundKeyState.Down, _entityManager.GetComponent<TransformComponent>(entity).Coordinates, args.PointerLocation, entity);
+                    BoundKeyState.Down, _entityManager.GetComponent<TransformComponent>(entity.Value).Coordinates, args.PointerLocation, entity.Value);
 
                 var session = _playerManager.LocalPlayer?.Session;
                 if (session != null)
@@ -314,7 +312,7 @@ namespace Content.Client.ContextMenu.UI
                 element.SubMenu.Dispose();
                 element.SubMenu = null;
                 element.CountLabel.Visible = false;
-                Elements[entity] = element;
+                Elements[entity.Value] = element;
             }
 
             // update the parent element, so that it's count and entity icon gets updated.
@@ -326,17 +324,17 @@ namespace Content.Client.ContextMenu.UI
         /// <summary>
         ///     Recursively look through a sub-menu and return the first entity.
         /// </summary>
-        private EntityUid GetFirstEntityOrNull(ContextMenuPopup? menu)
+        private EntityUid? GetFirstEntityOrNull(ContextMenuPopup? menu)
         {
             if (menu == null)
-                return default;
+                return null;
 
             foreach (var element in menu.MenuBody.Children)
             {
                 if (element is not EntityMenuElement entityElement)
                     continue;
 
-                if (entityElement.Entity != default)
+                if (entityElement.Entity != null)
                 {
                     if (!_entityManager.Deleted(entityElement.Entity))
                         return entityElement.Entity;
@@ -345,11 +343,11 @@ namespace Content.Client.ContextMenu.UI
 
                 // if the element has no entity, its a group of entities with another attached sub-menu.
                 var entity = GetFirstEntityOrNull(entityElement.SubMenu);
-                if (entity != default)
+                if (entity != null)
                     return entity;
             }
 
-            return default;
+            return null;
         }
 
         public override void OpenSubMenu(ContextMenuElement element)

Content.Client/DoAfter/DoAfterSystem.cs

@@ -118,8 +118,8 @@ namespace Content.Client.DoAfter
 
                     if (doAfter.BreakOnTargetMove)
                     {
-                        if (EntityManager.EntityExists(doAfter.TargetUid) &&
+                        if (!EntityManager.Deleted(doAfter.Target) &&
-                            !Transform(doAfter.TargetUid).Coordinates.InRange(EntityManager, doAfter.TargetGrid,
+                            !Transform(doAfter.Target.Value).Coordinates.InRange(EntityManager, doAfter.TargetGrid,
                                 doAfter.MovementThreshold))
                         {
                             comp.Cancel(id, currentTime);

Content.Client/Popups/PopupSystem.cs

@@ -51,7 +51,7 @@ namespace Content.Client.Popups
             PopupMessage(message, _eyeManager.CoordinatesToScreen(transform.Coordinates));
         }
 
-        public void PopupMessage(string message, ScreenCoordinates coordinates, EntityUid entity = default)
+        public void PopupMessage(string message, ScreenCoordinates coordinates, EntityUid? entity = null)
         {
             var label = new PopupLabel(_eyeManager, EntityManager)
             {
@@ -146,7 +146,7 @@ namespace Content.Client.Popups
 
             public float TimeLeft { get; private set; }
             public Vector2 InitialPos { get; set; }
-            public EntityUid Entity { get; set; }
+            public EntityUid? Entity { get; set; }
 
             public PopupLabel(IEyeManager eyeManager, IEntityManager entityManager)
             {
@@ -161,9 +161,9 @@ namespace Content.Client.Popups
             {
                 TimeLeft += eventArgs.DeltaSeconds;
 
-                var position = Entity == default
+                var position = Entity == null
                     ? InitialPos
-                    : (_eyeManager.CoordinatesToScreen(_entityManager.GetComponent<TransformComponent>(Entity).Coordinates).Position / UIScale) - DesiredSize / 2;
+                    : (_eyeManager.CoordinatesToScreen(_entityManager.GetComponent<TransformComponent>(Entity.Value).Coordinates).Position / UIScale) - DesiredSize / 2;
 
                 LayoutContainer.SetPosition(this, position - (0, 20 * (TimeLeft * TimeLeft + TimeLeft)));
 

Content.Client/Viewport/GameScreenBase.cs

@@ -44,7 +44,7 @@ namespace Content.Client.Viewport
 
         private IEventBus _eventBus => _entityManager.EventBus;
 
-        private EntityUid _lastHoveredEntity;
+        private EntityUid? _lastHoveredEntity;
 
         private bool _outlineEnabled = true;
 
@@ -84,7 +84,7 @@ namespace Content.Client.Viewport
             // lead to extremely thick outlines in the other viewports. Fixing this probably requires changing how the
             // hover outline works, so that it only highlights the entity in a single viewport.
 
-            EntityUid entityToClick = default;
+            EntityUid? entityToClick = null;
             var renderScale = 1;
             if (UserInterfaceManager.CurrentlyHovered is IViewportControl vp)
             {
@@ -107,15 +107,15 @@ namespace Content.Client.Viewport
             }
 
             var inRange = false;
-            if (localPlayer.ControlledEntity != default && entityToClick != default)
+            if (localPlayer.ControlledEntity != null && entityToClick != null)
             {
-                inRange = localPlayer.InRangeUnobstructed(entityToClick, ignoreInsideBlocker: true);
+                inRange = localPlayer.InRangeUnobstructed(entityToClick.Value, ignoreInsideBlocker: true);
             }
 
             InteractionOutlineComponent? outline;
             if(!_outlineEnabled || !ConfigurationManager.GetCVar(CCVars.OutlineEnabled))
             {
-                if(entityToClick != default && _entityManager.TryGetComponent(entityToClick, out outline))
+                if(entityToClick != null && _entityManager.TryGetComponent(entityToClick, out outline))
                 {
                     outline.OnMouseLeave(); //Prevent outline remains from persisting post command.
                 }
@@ -124,7 +124,7 @@ namespace Content.Client.Viewport
 
             if (entityToClick == _lastHoveredEntity)
             {
-                if (entityToClick != default && _entityManager.TryGetComponent(entityToClick, out outline))
+                if (entityToClick != null && _entityManager.TryGetComponent(entityToClick, out outline))
                 {
                     outline.UpdateInRange(inRange, renderScale);
                 }
@@ -132,7 +132,7 @@ namespace Content.Client.Viewport
                 return;
             }
 
-            if (_lastHoveredEntity != default && !_entityManager.Deleted(_lastHoveredEntity) &&
+            if (_lastHoveredEntity != null && !_entityManager.Deleted(_lastHoveredEntity) &&
                 _entityManager.TryGetComponent(_lastHoveredEntity, out outline))
             {
                 outline.OnMouseLeave();
@@ -140,16 +140,16 @@ namespace Content.Client.Viewport
 
             _lastHoveredEntity = entityToClick;
 
-            if (_lastHoveredEntity != default && _entityManager.TryGetComponent(_lastHoveredEntity, out outline))
+            if (_lastHoveredEntity != null && _entityManager.TryGetComponent(_lastHoveredEntity, out outline))
             {
                 outline.OnMouseEnter(inRange, renderScale);
             }
         }
 
-        public EntityUid GetEntityUnderPosition(MapCoordinates coordinates)
+        public EntityUid? GetEntityUnderPosition(MapCoordinates coordinates)
         {
             var entitiesUnderPosition = GetEntitiesUnderPosition(coordinates);
-            return entitiesUnderPosition.Count > 0 ? entitiesUnderPosition[0] : default;
+            return entitiesUnderPosition.Count > 0 ? entitiesUnderPosition[0] : null;
         }
 
         public IList<EntityUid> GetEntitiesUnderPosition(EntityCoordinates coordinates)
@@ -257,7 +257,7 @@ namespace Content.Client.Viewport
             var funcId = InputManager.NetworkBindMap.KeyFunctionID(func);
 
             EntityCoordinates coordinates = default;
-            EntityUid entityToClick = default;
+            EntityUid? entityToClick = null;
             if (args.Viewport is IViewportControl vp)
             {
                 var mousePosWorld = vp.ScreenToMap(kArgs.PointerLocation.Position);
@@ -269,7 +269,7 @@ namespace Content.Client.Viewport
 
             var message = new FullInputCmdMessage(Timing.CurTick, Timing.TickFraction, funcId, kArgs.State,
                 coordinates , kArgs.PointerLocation,
-                entityToClick);
+                entityToClick ?? default); // TODO make entityUid nullable
 
             // client side command handlers will always be sent the local player session.
             var session = PlayerManager.LocalPlayer?.Session;

Content.Client/Wall/Components/LowWallComponent.cs

@@ -64,10 +64,11 @@ namespace Content.Client.Wall.Components
         {
             base.Shutdown();
 
-            EntityUid tempQualifier = _overlayEntity;
+            // _overlayEntity is non-nullable as it is set on startup.
-            if (tempQualifier != null)
+            // Should also never be default but might as well check.
+            if (_overlayEntity.Valid)
             {
-                _entMan.DeleteEntity(tempQualifier);
+                _entMan.DeleteEntity(_overlayEntity);
             }
         }
 

Content.Server/AI/LoadBalancer/AiActionRequestJob.cs

@@ -39,7 +39,7 @@ namespace Content.Server.AI.LoadBalancer
 
             var entity = _request.Context.GetState<SelfState>().GetValue();
 
-            if (entity == null || !IoCManager.Resolve<IEntityManager>().HasComponent<AiControllerComponent>(entity))
+            if (!IoCManager.Resolve<IEntityManager>().HasComponent<AiControllerComponent>(entity))
             {
                 return null;
             }

Content.Server/AI/Utility/Considerations/ActionBlocker/CanMoveCon.cs

@@ -12,7 +12,7 @@ namespace Content.Server.AI.Utility.Considerations.ActionBlocker
         {
             var self = context.GetState<SelfState>().GetValue();
 
-            if (self == null || !EntitySystem.Get<ActionBlockerSystem>().CanMove(self))
+            if (!EntitySystem.Get<ActionBlockerSystem>().CanMove(self))
             {
                 return 0.0f;
             }

Content.Server/AI/Utility/Considerations/Containers/TargetAccessibleCon.cs

@@ -24,7 +24,7 @@ namespace Content.Server.AI.Utility.Considerations.Containers
                 return 0.0f;
             }
 
-            if (target.TryGetContainer(out var container))
+            if (target!.Value.TryGetContainer(out var container))
             {
                 if (entMan.TryGetComponent(container.Owner, out EntityStorageComponent? storageComponent))
                 {
@@ -43,12 +43,7 @@ namespace Content.Server.AI.Utility.Considerations.Containers
 
             var owner = context.GetState<SelfState>().GetValue();
 
-            if (owner == null)
+            return EntitySystem.Get<AiReachableSystem>().CanAccess(owner, target.Value, SharedInteractionSystem.InteractionRange) ? 1.0f : 0.0f;
-            {
-                return 0;
-            }
-
-            return EntitySystem.Get<AiReachableSystem>().CanAccess(owner, target, SharedInteractionSystem.InteractionRange) ? 1.0f : 0.0f;
         }
     }
 }

Content.Server/AI/Utility/Considerations/Nutrition/Drink/DrinkValueCon.cs

@@ -15,7 +15,7 @@ namespace Content.Server.AI.Utility.Considerations.Nutrition.Drink
 
             if (target == null
                 || IoCManager.Resolve<IEntityManager>().Deleted(target)
-                || !EntitySystem.Get<SolutionContainerSystem>().TryGetSolution(target, DrinkComponent.DefaultSolutionName, out var drink))
+                || !EntitySystem.Get<SolutionContainerSystem>().TryGetSolution(target.Value, DrinkComponent.DefaultSolutionName, out var drink))
             {
                 return 0.0f;
             }

Content.Server/AI/Utility/Considerations/Nutrition/Drink/ThirstCon.cs

@@ -13,7 +13,7 @@ namespace Content.Server.AI.Utility.Considerations.Nutrition.Drink
         {
             var owner = context.GetState<SelfState>().GetValue();
 
-            if (owner == null || !IoCManager.Resolve<IEntityManager>().TryGetComponent(owner, out ThirstComponent? thirst))
+            if (!IoCManager.Resolve<IEntityManager>().TryGetComponent(owner, out ThirstComponent? thirst))
             {
                 return 0.0f;
             }

Content.Server/AI/Utility/Considerations/Nutrition/Food/FoodValueCon.cs

@@ -13,8 +13,8 @@ namespace Content.Server.AI.Utility.Considerations.Nutrition.Food
         {
             var target = context.GetState<TargetEntityState>().GetValue();
 
-            if (target == null || !IoCManager.Resolve<IEntityManager>().TryGetComponent<FoodComponent?>(target, out var foodComp)
+            if (target == null || !IoCManager.Resolve<IEntityManager>().TryGetComponent<FoodComponent?>(target.Value, out var foodComp)
-                               || !EntitySystem.Get<SolutionContainerSystem>().TryGetSolution(target, foodComp.SolutionName, out var food))
+                               || !EntitySystem.Get<SolutionContainerSystem>().TryGetSolution(target.Value, foodComp.SolutionName, out var food))
             {
                 return 0.0f;
             }

Content.Server/AI/Utility/Considerations/Nutrition/Food/HungerCon.cs

@@ -14,7 +14,7 @@ namespace Content.Server.AI.Utility.Considerations.Nutrition.Food
         {
             var owner = context.GetState<SelfState>().GetValue();
 
-            if (owner == null || !IoCManager.Resolve<IEntityManager>().TryGetComponent(owner, out HungerComponent? hunger))
+            if (!IoCManager.Resolve<IEntityManager>().TryGetComponent(owner, out HungerComponent? hunger))
             {
                 return 0.0f;
             }

Content.Server/AI/WorldState/States/Combat/WeaponEntityState.cs

@@ -4,13 +4,13 @@ using Robust.Shared.GameObjects;
 namespace Content.Server.AI.WorldState.States.Combat
 {
     [UsedImplicitly]
-    public sealed class WeaponEntityState : PlanningStateData<EntityUid>
+    public sealed class WeaponEntityState : PlanningStateData<EntityUid?>
     {
         // Similar to TargetEntity
         public override string Name => "WeaponEntity";
         public override void Reset()
         {
-            Value = default;
+            Value = null;
         }
     }
 }

Content.Server/AI/WorldState/States/Inventory/EquippedEntityState.cs

@@ -9,18 +9,13 @@ namespace Content.Server.AI.WorldState.States.Inventory
     /// AKA what's in active hand
     /// </summary>
     [UsedImplicitly]
-    public sealed class EquippedEntityState : StateData<EntityUid>
+    public sealed class EquippedEntityState : StateData<EntityUid?>
     {
         public override string Name => "EquippedEntity";
 
-        public override EntityUid GetValue()
+        public override EntityUid? GetValue()
         {
-            if (!IoCManager.Resolve<IEntityManager>().TryGetComponent(Owner, out HandsComponent? handsComponent))
+            return IoCManager.Resolve<IEntityManager>().GetComponentOrNull<HandsComponent>(Owner)?.GetActiveHand?.Owner;
-            {
-                return default;
-            }
-
-            return handsComponent.GetActiveHand?.Owner ?? default;
         }
     }
 }

Content.Server/AI/WorldState/States/Movement/MoveTargetState.cs

@@ -4,12 +4,12 @@ using Robust.Shared.GameObjects;
 namespace Content.Server.AI.WorldState.States.Movement
 {
     [UsedImplicitly]
-    public sealed class MoveTargetState : PlanningStateData<EntityUid>
+    public sealed class MoveTargetState : PlanningStateData<EntityUid?>
     {
         public override string Name => "MoveTarget";
         public override void Reset()
         {
-            Value = default;
+            Value = null;
         }
     }
 }

Content.Server/AI/WorldState/States/TargetEntityState.cs

@@ -7,13 +7,13 @@ namespace Content.Server.AI.WorldState.States
     /// Could be target item to equip, target to attack, etc.
     /// </summary>
     [UsedImplicitly]
-    public sealed class TargetEntityState : PlanningStateData<EntityUid>
+    public sealed class TargetEntityState : PlanningStateData<EntityUid?>
     {
         public override string Name => "TargetEntity";
 
         public override void Reset()
         {
-            Value = default;
+            Value = null;
         }
     }
 }

Content.Server/Body/Components/InternalsComponent.cs

@@ -11,15 +11,15 @@ namespace Content.Server.Body.Components
         [Dependency] private readonly IEntityManager _entMan = default!;
 
         public override string Name => "Internals";
-        [ViewVariables] public EntityUid GasTankEntity { get; set; }
+        [ViewVariables] public EntityUid? GasTankEntity { get; set; }
-        [ViewVariables] public EntityUid BreathToolEntity { get; set; }
+        [ViewVariables] public EntityUid? BreathToolEntity { get; set; }
 
         public void DisconnectBreathTool()
         {
             var old = BreathToolEntity;
-            BreathToolEntity = default;
+            BreathToolEntity = null;
 
-            if (old != default && _entMan.TryGetComponent(old, out BreathToolComponent? breathTool) )
+            if (_entMan.TryGetComponent(old, out BreathToolComponent? breathTool) )
             {
                 breathTool.DisconnectInternals();
                 DisconnectTank();
@@ -28,7 +28,7 @@ namespace Content.Server.Body.Components
 
         public void ConnectBreathTool(EntityUid toolEntity)
         {
-            if (BreathToolEntity != default && _entMan.TryGetComponent(BreathToolEntity, out BreathToolComponent? tool))
+            if (_entMan.TryGetComponent(BreathToolEntity, out BreathToolComponent? tool))
             {
                 tool.DisconnectInternals();
             }
@@ -38,20 +38,20 @@ namespace Content.Server.Body.Components
 
         public void DisconnectTank()
         {
-            if (GasTankEntity != default && _entMan.TryGetComponent(GasTankEntity, out GasTankComponent? tank))
+            if (_entMan.TryGetComponent(GasTankEntity, out GasTankComponent? tank))
             {
                 tank.DisconnectFromInternals(Owner);
             }
 
-            GasTankEntity = default;
+            GasTankEntity = null;
         }
 
         public bool TryConnectTank(EntityUid tankEntity)
         {
-            if (BreathToolEntity == default)
+            if (BreathToolEntity == null)
                 return false;
 
-            if (GasTankEntity != default && _entMan.TryGetComponent(GasTankEntity, out GasTankComponent? tank))
+            if (_entMan.TryGetComponent(GasTankEntity, out GasTankComponent? tank))
             {
                 tank.DisconnectFromInternals(Owner);
             }
@@ -62,12 +62,10 @@ namespace Content.Server.Body.Components
 
         public bool AreInternalsWorking()
         {
-            return BreathToolEntity != default &&
+            return _entMan.TryGetComponent(BreathToolEntity, out BreathToolComponent? breathTool) &&
-                   GasTankEntity != default &&
-                   _entMan.TryGetComponent(BreathToolEntity, out BreathToolComponent? breathTool) &&
                    breathTool.IsFunctional &&
                    _entMan.TryGetComponent(GasTankEntity, out GasTankComponent? gasTank) &&
-                   gasTank.Air != default;
+                   gasTank.Air != null;
         }
 
     }

Content.Server/Botany/Seed.cs

@@ -291,9 +291,6 @@ namespace Content.Server.Botany
         {
             AddToDatabase();
 
-            if (user == null)
-                return Enumerable.Empty<EntityUid>();
-
             if (ProductPrototypes == null || ProductPrototypes.Count == 0 || Yield <= 0)
             {
                 user.PopupMessageCursor(Loc.GetString("botany-harvest-fail-message"));

Content.Server/Climbing/Components/ClimbableComponent.cs

@@ -115,7 +115,7 @@ namespace Content.Server.Climbing.Components
                 return false;
             }
 
-            if (target == null || !_entities.HasComponent<ClimbingComponent>(dragged))
+            if (!_entities.HasComponent<ClimbingComponent>(dragged))
             {
                 reason = Loc.GetString("comp-climbable-cant-climb");
                 return false;

Content.Server/Clothing/MagbootsSystem.cs

@@ -25,7 +25,7 @@ namespace Content.Server.Clothing
 
         private void AddToggleVerb(EntityUid uid, MagbootsComponent component, GetActivationVerbsEvent args)
         {
-            if (args.User == null || !args.CanAccess || !args.CanInteract)
+            if (!args.CanAccess || !args.CanInteract)
                 return;
 
             Verb verb = new();

Content.Server/Disposal/Unit/Components/DisposalUnitComponent.cs

@@ -90,11 +90,6 @@ namespace Content.Server.Disposal.Unit.Components
 
         private bool PlayerCanUse(EntityUid player)
         {
-            if (player == null)
-            {
-                return false;
-            }
-
             var actionBlocker = EntitySystem.Get<ActionBlockerSystem>();
 
             if (!actionBlocker.CanInteract(player) ||

Content.Server/Doors/Components/ServerDoorComponent.cs

@@ -275,19 +275,19 @@ namespace Content.Server.Doors.Components
 
         #region Opening
 
-        public void TryOpen(EntityUid user = default)
+        public void TryOpen(EntityUid? user = null)
         {
             var msg = new DoorOpenAttemptEvent();
             _entMan.EventBus.RaiseLocalEvent(Owner, msg);
 
             if (msg.Cancelled) return;
 
-            if (!user.Valid)
+            if (user == null)
             {
                 // a machine opened it or something, idk
                 Open();
             }
-            else if (CanOpenByEntity(user))
+            else if (CanOpenByEntity(user.Value))
             {
                 Open();
 
@@ -422,14 +422,14 @@ namespace Content.Server.Doors.Components
 
         #region Closing
 
-        public void TryClose(EntityUid user = default)
+        public void TryClose(EntityUid? user = null)
         {
             var msg = new DoorCloseAttemptEvent();
             _entMan.EventBus.RaiseLocalEvent(Owner, msg);
 
             if (msg.Cancelled) return;
 
-            if (user != default && !CanCloseByEntity(user))
+            if (user != null && !CanCloseByEntity(user.Value))
             {
                 Deny();
                 return;

Content.Server/Hands/Components/HandsComponent.cs

@@ -99,12 +99,8 @@ namespace Content.Server.Hands.Components
             var source = @event.Source;
             var target = @event.Target;
 
-            if (source != null)
-            {
             SoundSystem.Play(Filter.Pvs(source), _disarmedSound.GetSound(), source, AudioHelpers.WithVariation(0.025f));
 
-                if (target != null)
-                {
             if (ActiveHand != null && Drop(ActiveHand, false))
             {
                 source.PopupMessageOtherClients(Loc.GetString("hands-component-disarm-success-others-message", ("disarmer", Name: _entities.GetComponent<MetaDataComponent>(source).EntityName), ("disarmed", Name: _entities.GetComponent<MetaDataComponent>(target).EntityName)));
@@ -115,8 +111,6 @@ namespace Content.Server.Hands.Components
                 source.PopupMessageOtherClients(Loc.GetString("hands-component-shove-success-others-message", ("shover", Name: _entities.GetComponent<MetaDataComponent>(source).EntityName), ("shoved", Name: _entities.GetComponent<MetaDataComponent>(target).EntityName)));
                 source.PopupMessageCursor(Loc.GetString("hands-component-shove-success-message", ("shoved", Name: _entities.GetComponent<MetaDataComponent>(target).EntityName)));
             }
-                }
-            }
 
             return true;
         }

Content.Server/Light/EntitySystems/LightReplacerSystem.cs

@@ -67,8 +67,6 @@ namespace Content.Server.Light.EntitySystems
             // standard interaction checks
             if (!_blocker.CanInteract(eventArgs.User)) return;
 
-            if (eventArgs.Used != null)
-            {
             var usedUid = eventArgs.Used;
 
             // want to insert a new light bulb?
@@ -78,7 +76,6 @@ namespace Content.Server.Light.EntitySystems
             else if (EntityManager.TryGetComponent(usedUid, out ServerStorageComponent? storage))
                 eventArgs.Handled = TryInsertBulbsFromStorage(uid, usedUid, eventArgs.User, component, storage);
         }
-        }
 
         /// <summary>
         ///     Try to replace a light bulb in <paramref name="fixtureUid"/>
@@ -108,7 +105,7 @@ namespace Content.Server.Light.EntitySystems
                 (e) => EntityManager.GetComponentOrNull<LightBulbComponent>(e)?.Type == fixture.BulbType);
 
             // found bulb in inserted storage
-            if (bulb != null)
+            if (bulb.Valid) // FirstOrDefault can return default/invalid uid.
             {
                 // try to remove it
                 var hasRemoved = replacer.InsertedBulbs.Remove(bulb);

Content.Server/PAI/PAISystem.cs

@@ -129,7 +129,7 @@ namespace Content.Server.PAI
 
         private void AddWipeVerb(EntityUid uid, PAIComponent pai, GetActivationVerbsEvent args)
         {
-            if (args.User == null || !args.CanAccess || !args.CanInteract)
+            if (!args.CanAccess || !args.CanInteract)
                 return;
 
             if (EntityManager.TryGetComponent<MindComponent>(uid, out var mind) && mind.HasMind)

Content.Server/PowerCell/Components/PowerCellSlotComponent.cs

@@ -128,7 +128,7 @@ namespace Content.Server.PowerCell.Components
         /// <param name="user">(optional) the user to give the removed cell to.</param>
         /// <param name="playSound">Should <see cref="CellRemoveSound"/> be played upon removal?</param>
         /// <returns>The cell component of the entity that was removed, or null if removal failed.</returns>
-        public PowerCellComponent? EjectCell(EntityUid user, bool playSound = true)
+        public PowerCellComponent? EjectCell(EntityUid? user = null, bool playSound = true)
         {
             var cell = Cell;
             if (cell == null || !CanRemoveCell) return null;
@@ -138,7 +138,7 @@ namespace Content.Server.PowerCell.Components
             {
                 if (!_entities.TryGetComponent(user, out HandsComponent? hands) || !hands.PutInHand(_entities.GetComponent<ItemComponent>(cell.Owner)))
                 {
-                    _entities.GetComponent<TransformComponent>(cell.Owner).Coordinates = _entities.GetComponent<TransformComponent>(user).Coordinates;
+                    _entities.GetComponent<TransformComponent>(cell.Owner).Coordinates = _entities.GetComponent<TransformComponent>(user.Value).Coordinates;
                 }
             }
             else

Content.Server/RCD/Systems/RCDSystem.cs

@@ -235,11 +235,8 @@ namespace Content.Server.RCD.Systems
             mode = (++mode) % _modes.Length; //Then, do a rollover on the value so it doesnt hit an invalid state
             rcd.Mode = (RcdMode) mode; //Finally, cast the newly acquired int mode to an RCDmode so we can use it.
 
-            if (user != null)
-            {
             var msg = Loc.GetString("rcd-component-change-mode", ("mode", rcd.Mode.ToString()));
             rcd.Owner.PopupMessage(user, msg); //Prints an overhead message above the RCD
         }
     }
 }
-}

Content.Server/Stack/StackSystem.cs

@@ -42,7 +42,7 @@ namespace Content.Server.Stack
         public EntityUid? Split(EntityUid uid, int amount, EntityCoordinates spawnPosition, SharedStackComponent? stack = null)
         {
             if (!Resolve(uid, ref stack))
-                return default;
+                return null;
 
             // Get a prototype ID to spawn the new entity. Null is also valid, although it should rarely be picked...
             var prototype = _prototypeManager.TryIndex<StackPrototype>(stack.StackTypeId, out var stackType)
@@ -51,7 +51,7 @@ namespace Content.Server.Stack
 
             // Try to remove the amount of things we want to split from the original stack...
             if (!Use(uid, amount, stack))
-                return default;
+                return null;
 
             // Set the output parameter in the event instance to the newly split stack.
             var entity = Spawn(prototype, spawnPosition);

Content.Server/Storage/Components/CursedEntityStorageComponent.cs

@@ -37,9 +37,9 @@ namespace Content.Server.Storage.Components
             if (lockers.Contains(Owner))
                 lockers.Remove(Owner);
 
-            var lockerEnt = _robustRandom.Pick(lockers);
+            if (lockers.Count == 0) return;
 
-            if (lockerEnt == null) return; // No valid lockers anywhere.
+            var lockerEnt = _robustRandom.Pick(lockers);
 
             var locker = _entMan.GetComponent<EntityStorageComponent>(lockerEnt);
 

Content.Server/Storage/EntitySystems/SpawnItemsOnUseSystem.cs

@@ -27,7 +27,7 @@ namespace Content.Server.Storage.EntitySystems
                 return;
 
             var alreadySpawnedGroups = new List<string>();
-            EntityUid entityToPlaceInHands = default;
+            EntityUid? entityToPlaceInHands = null;
             foreach (var storageItem in component.Items)
             {
                 if (!string.IsNullOrEmpty(storageItem.GroupId) &&
@@ -57,10 +57,10 @@ namespace Content.Server.Storage.EntitySystems
                 EntityManager.DeleteEntity(uid);
             }
 
-            if (entityToPlaceInHands != default
+            if (entityToPlaceInHands != null
                 && EntityManager.TryGetComponent<SharedHandsComponent?>(args.User, out var hands))
             {
-                hands.TryPutInAnyHand(entityToPlaceInHands);
+                hands.TryPutInAnyHand(entityToPlaceInHands.Value);
             }
         }
     }

Content.Server/Stunnable/StunSystem.cs

@@ -40,18 +40,12 @@ namespace Content.Server.Stunnable
             var source = args.Source;
             var target = args.Target;
 
-            if (source != null)
-            {
             var knock = EntityManager.GetComponent<KnockedDownComponent>(uid);
             SoundSystem.Play(Filter.Pvs(source), knock.StunAttemptSound.GetSound(), source, AudioHelpers.WithVariation(0.025f));
 
-                if (target != null)
-                {
             // TODO: Use PopupSystem
-                    source.PopupMessageOtherClients(Loc.GetString("stunned-component-disarm-success-others", ("source", Name: EntityManager.GetComponent<MetaDataComponent>(source).EntityName), ("target", Name: EntityManager.GetComponent<MetaDataComponent>(target).EntityName)));
+            source.PopupMessageOtherClients(Loc.GetString("stunned-component-disarm-success-others", ("source", Name(source)), ("target", Name(target))));
-                    source.PopupMessageCursor(Loc.GetString("stunned-component-disarm-success", ("target", Name: EntityManager.GetComponent<MetaDataComponent>(target).EntityName)));
+            source.PopupMessageCursor(Loc.GetString("stunned-component-disarm-success", ("target", Name(target))));
-                }
-            }
 
             _adminLogSystem.Add(LogType.DisarmedKnockdown, LogImpact.Medium, $"{ToPrettyString(args.Source):user} knocked down {ToPrettyString(args.Target):target}");
 

Content.Server/Verbs/Commands/InvokeVerbCommand.cs

@@ -29,7 +29,7 @@ namespace Content.Server.Verbs.Commands
             var verbSystem = EntitySystem.Get<SharedVerbSystem>();
 
             // get the 'player' entity (defaulting to command user, otherwise uses a uid)
-            EntityUid playerEntity = default;
+            EntityUid? playerEntity = null;
             if (!int.TryParse(args[0], out var intPlayerUid))
             {
                 if (args[0] == "self" && shell.Player?.AttachedEntity != null)
@@ -54,7 +54,7 @@ namespace Content.Server.Verbs.Commands
                 return;
             }
 
-            if (playerEntity == default)
+            if (playerEntity == null)
             {
                 shell.WriteError(Loc.GetString("invoke-verb-command-invalid-player-entity"));
                 return;
@@ -68,14 +68,14 @@ namespace Content.Server.Verbs.Commands
             }
 
             var verbName = args[2].ToLowerInvariant();
-            var verbs = verbSystem.GetLocalVerbs(target, playerEntity, VerbType.All, true);
+            var verbs = verbSystem.GetLocalVerbs(target, playerEntity.Value, VerbType.All, true);
 
             if ((Enum.TryParse(typeof(VerbType), verbName, ignoreCase: true, out var vtype) &&
                 vtype is VerbType key) &&
                 verbs.TryGetValue(key, out var vset) &&
                 vset.Any())
             {
-                verbSystem.ExecuteVerb(vset.First(), playerEntity, target, forced: true);
+                verbSystem.ExecuteVerb(vset.First(), playerEntity.Value, target, forced: true);
                 shell.WriteLine(Loc.GetString("invoke-verb-command-success", ("verb", verbName), ("target", target), ("player", playerEntity)));
                 return;
             }
@@ -86,7 +86,7 @@ namespace Content.Server.Verbs.Commands
                 {
                     if (verb.Text.ToLowerInvariant() == verbName)
                     {
-                        verbSystem.ExecuteVerb(verb, playerEntity, target, forced: true);
+                        verbSystem.ExecuteVerb(verb, playerEntity.Value, target, forced: true);
                         shell.WriteLine(Loc.GetString("invoke-verb-command-success", ("verb", verb.Text), ("target", target), ("player", playerEntity)));
                         return;
                     }

Content.Server/Weapon/Ranged/Ammunition/Components/RangedMagazineComponent.cs

@@ -120,7 +120,7 @@ namespace Content.Server.Weapon.Ranged.Ammunition.Components
 
         public EntityUid? TakeAmmo()
         {
-            EntityUid ammo = default;
+            EntityUid? ammo = null;
             // If anything's spawned use that first, otherwise use the fill prototype as a fallback (if we have spawn count left)
             if (_spawnedAmmo.TryPop(out var entity))
             {

Content.Server/Weapon/Ranged/Barrels/Components/ServerBatteryBarrelComponent.cs

@@ -133,13 +133,13 @@ namespace Content.Server.Weapon.Ranged.Barrels.Components
 
             if (powerCellEntity == null)
             {
-                return default;
+                return null;
             }
 
             var capacitor = _entities.GetComponent<BatteryComponent>(powerCellEntity.Value);
             if (capacitor.CurrentCharge < _lowerChargeLimit)
             {
-                return default;
+                return null;
             }
 
             // Can fire confirmed
@@ -149,7 +149,7 @@ namespace Content.Server.Weapon.Ranged.Barrels.Components
             if (capacitor.UseCharge(chargeChange) < _lowerChargeLimit)
             {
                 // Handling of funny exploding cells.
-                return default;
+                return null;
             }
             var energyRatio = chargeChange / _baseFireCost;
 

Content.Server/Weapon/Ranged/Barrels/Components/ServerMagazineBarrelComponent.cs

@@ -193,19 +193,20 @@ namespace Content.Server.Weapon.Ranged.Barrels.Components
 
         public override EntityUid? PeekAmmo()
         {
-            return BoltOpen ? default : _chamberContainer.ContainedEntity;
+            return BoltOpen ? null : _chamberContainer.ContainedEntity;
         }
 
         public override EntityUid? TakeProjectile(EntityCoordinates spawnAt)
         {
             if (BoltOpen)
             {
-                return default;
+                return null;
             }
-            var entity = _chamberContainer.ContainedEntity ?? default;
+            var entity = _chamberContainer.ContainedEntity;
 
             Cycle();
-            return entity != default ? EntitySystem.Get<GunSystem>().TakeBullet(_entities.GetComponent<AmmoComponent>(entity), spawnAt) : null;
+
+            return entity != null ? EntitySystem.Get<GunSystem>().TakeBullet(_entities.GetComponent<AmmoComponent>(entity.Value), spawnAt) : null;
         }
 
         private void Cycle(bool manual = false)
@@ -296,7 +297,7 @@ namespace Content.Server.Weapon.Ranged.Barrels.Components
             }
 
             // Try and pull a round from the magazine to replace the chamber if possible
-            var magazine = MagazineContainer.ContainedEntity ?? default;
+            var magazine = MagazineContainer.ContainedEntity;
 
             if (_entities.GetComponentOrNull<RangedMagazineComponent>(magazine)?.TakeAmmo() is not {Valid: true} nextRound)
             {
@@ -305,11 +306,11 @@ namespace Content.Server.Weapon.Ranged.Barrels.Components
 
             _chamberContainer.Insert(nextRound);
 
-            if (_autoEjectMag && magazine != null && _entities.GetComponent<RangedMagazineComponent>(magazine).ShotsLeft == 0)
+            if (_autoEjectMag && magazine != null && _entities.GetComponent<RangedMagazineComponent>(magazine.Value).ShotsLeft == 0)
             {
                 SoundSystem.Play(Filter.Pvs(Owner), _soundAutoEject.GetSound(), Owner, AudioParams.Default.WithVolume(-2));
 
-                MagazineContainer.Remove(magazine);
+                MagazineContainer.Remove(magazine.Value);
 #pragma warning disable 618
                 SendNetworkMessage(new MagazineAutoEjectMessage());
 #pragma warning restore 618

Content.Server/Wieldable/WieldableSystem.cs

@@ -151,9 +151,10 @@ namespace Content.Server.Wieldable
 
         private void OnItemWielded(EntityUid uid, WieldableComponent component, ItemWieldedEvent args)
         {
-            if (args.User == default)
+            if (args.User == null)
                 return;
-            if (!CanWield(uid, component, args.User) || component.Wielded)
+
+            if (!CanWield(uid, component, args.User.Value) || component.Wielded)
                 return;
 
             if (EntityManager.TryGetComponent<ItemComponent>(uid, out var item))
@@ -171,16 +172,16 @@ namespace Content.Server.Wieldable
 
             for (var i = 0; i < component.FreeHandsRequired; i++)
             {
-                _virtualItemSystem.TrySpawnVirtualItemInHand(uid, args.User);
+                _virtualItemSystem.TrySpawnVirtualItemInHand(uid, args.User.Value);
             }
 
-            args.User.PopupMessage(Loc.GetString("wieldable-component-successful-wield",
+            args.User.Value.PopupMessage(Loc.GetString("wieldable-component-successful-wield",
                 ("item", uid)));
         }
 
         private void OnItemUnwielded(EntityUid uid, WieldableComponent component, ItemUnwieldedEvent args)
         {
-            if (args.User == default)
+            if (args.User == null)
                 return;
             if (!component.Wielded)
                 return;
@@ -200,11 +201,11 @@ namespace Content.Server.Wieldable
                         component.UnwieldSound.GetSound());
                 }
 
-                args.User.PopupMessage(Loc.GetString("wieldable-component-failed-wield",
+                args.User.Value.PopupMessage(Loc.GetString("wieldable-component-failed-wield",
                     ("item", uid)));
             }
 
-            _virtualItemSystem.DeleteInHandsMatching(args.User, uid);
+            _virtualItemSystem.DeleteInHandsMatching(args.User.Value, uid);
         }
 
         private void OnItemLeaveHand(EntityUid uid, WieldableComponent component, UnequippedHandEvent args)
@@ -245,9 +246,9 @@ namespace Content.Server.Wieldable
     /// </summary>
     public class ItemWieldedEvent : EntityEventArgs
     {
-        public EntityUid User;
+        public EntityUid? User;
 
-        public ItemWieldedEvent(EntityUid user = default)
+        public ItemWieldedEvent(EntityUid? user = null)
         {
             User = user;
         }
@@ -275,13 +276,13 @@ namespace Content.Server.Wieldable
     /// </summary>
     public class ItemUnwieldedEvent : EntityEventArgs
     {
-        public EntityUid User;
+        public EntityUid? User;
         /// <summary>
         ///     Whether the item is being forced to be unwielded, or if the player chose to unwield it themselves.
         /// </summary>
         public bool Force;
 
-        public ItemUnwieldedEvent(EntityUid user = default, bool force=false)
+        public ItemUnwieldedEvent(EntityUid? user = null, bool force=false)
         {
             User = user;
             Force = force;

Content.Shared/DoAfter/SharedDoAfterComponent.cs

@@ -52,7 +52,7 @@ namespace Content.Shared.DoAfter
 
         public EntityCoordinates TargetGrid { get; }
 
-        public EntityUid TargetUid { get; }
+        public EntityUid? Target { get; }
 
         public float Delay { get; }
 
@@ -63,7 +63,8 @@ namespace Content.Shared.DoAfter
 
         public float MovementThreshold { get; }
 
-        public ClientDoAfter(byte id, EntityCoordinates userGrid, EntityCoordinates targetGrid, TimeSpan startTime, float delay, bool breakOnUserMove, bool breakOnTargetMove, float movementThreshold, EntityUid targetUid = default)
+        public ClientDoAfter(byte id, EntityCoordinates userGrid, EntityCoordinates targetGrid, TimeSpan startTime,
+            float delay, bool breakOnUserMove, bool breakOnTargetMove, float movementThreshold, EntityUid? target = null)
         {
             ID = id;
             UserGrid = userGrid;
@@ -73,7 +74,7 @@ namespace Content.Shared.DoAfter
             BreakOnUserMove = breakOnUserMove;
             BreakOnTargetMove = breakOnTargetMove;
             MovementThreshold = movementThreshold;
-            TargetUid = targetUid;
+            Target = target;
         }
     }
 }

Content.Shared/Interaction/SharedInteractionSystem.cs

@@ -650,7 +650,7 @@ namespace Content.Shared.Interaction
         /// <param name="used"></param>
         public void TryUseInteraction(EntityUid user, EntityUid used, bool altInteract = false)
         {
-            if (user != null && used != null && _actionBlockerSystem.CanUse(user))
+            if (_actionBlockerSystem.CanUse(user))
             {
                 if (altInteract)
                     AltInteract(user, used);
@@ -820,7 +820,7 @@ namespace Content.Shared.Interaction
         /// </summary>
         public bool TryDroppedInteraction(EntityUid user, EntityUid item)
         {
-            if (user == null || item == null || !_actionBlockerSystem.CanDrop(user)) return false;
+            if (!_actionBlockerSystem.CanDrop(user)) return false;
 
             DroppedInteraction(user, item);
             return true;

Content.Shared/Verbs/SharedVerbSystem.cs

@@ -64,15 +64,17 @@ namespace Content.Shared.Verbs
             // call ActionBlocker checks, just cache it for the verb request.
             var canInteract = force || _actionBlockerSystem.CanInteract(user);
 
-            EntityUid @using = default;
+            EntityUid? @using = null;
-            if (EntityManager.TryGetComponent(user, out SharedHandsComponent? hands) && (force || _actionBlockerSystem.CanUse(user)))
+            if (TryComp(user, out SharedHandsComponent? hands) && (force || _actionBlockerSystem.CanUse(user)))
             {
-                hands.TryGetActiveHeldEntity(out @using);
+                // TODO Hands remove nullable (#5634)
+                hands.TryGetActiveHeldEntity(out var nonNullableUsing);
+                @using = nonNullableUsing;
 
                 // Check whether the "Held" entity is a virtual pull entity. If yes, set that as the entity being "Used".
                 // This allows you to do things like buckle a dragged person onto a surgery table, without click-dragging
                 // their sprite.
-                if (@using != default && EntityManager.TryGetComponent<HandVirtualItemComponent?>(@using, out var pull))
+                if (@using != null && TryComp(@using, out HandVirtualItemComponent? pull))
                 {
                     @using = pull.BlockingEntity;
                 }