Enable nullability in Content.Server (#3685)

Content.Server/GameObjects/EntitySystems/SignalLinkerSystem.cs

@@ -12,14 +12,7 @@ namespace Content.Server.GameObjects.EntitySystems
 {
     public class SignalLinkerSystem : EntitySystem
     {
-        private Dictionary<NetUserId, SignalTransmitterComponent> _transmitters;
-
-        public override void Initialize()
-        {
-            base.Initialize();
-
-            _transmitters = new Dictionary<NetUserId, SignalTransmitterComponent>();
-        }
+        private readonly Dictionary<NetUserId, SignalTransmitterComponent?> _transmitters = new();
 
         public bool SignalLinkerKeybind(NetUserId id, bool? enable)
         {
@@ -35,7 +28,9 @@ namespace Content.Server.GameObjects.EntitySystems
                 if (_transmitters.Count == 0)
                 {
                     CommandBinds.Builder
-                        .BindBefore(EngineKeyFunctions.Use, new PointerInputCmdHandler(HandleUse), typeof(InteractionSystem))
+                        .BindBefore(EngineKeyFunctions.Use,
+                            new PointerInputCmdHandler(HandleUse),
+                            typeof(InteractionSystem))
                         .Register<SignalLinkerSystem>();
                 }
 
@@ -59,8 +54,13 @@ namespace Content.Server.GameObjects.EntitySystems
             return enable.Value;
         }
 
-        private bool HandleUse(ICommonSession session, EntityCoordinates coords, EntityUid uid)
+        private bool HandleUse(ICommonSession? session, EntityCoordinates coords, EntityUid uid)
         {
+            if (session?.AttachedEntity == null)
+            {
+                return false;
+            }
+
             if (!_transmitters.TryGetValue(session.UserId, out var signalTransmitter))
             {
                 return false;
@@ -88,6 +88,5 @@ namespace Content.Server.GameObjects.EntitySystems
 
             return false;
         }
-
     }
 }