Added nullable to most Content.Shared files (#3238)

* Add nullable to some Content.Shared files.

* Use [NotNullWhen(true)]

* Undo adding now redundant !'s

* Forgot one

* Add a ton more nullable

* You can guess

* Fix some issues

* It actually compiles now

* Auto stash before merge of "null2" and "origin/master"

* I lied

* enable annotations -> enable

* Revert ActionBlockerSystem.cs to original

* Fix ActionBlockerSystem.cs

* More nullable

* Undo some added exclamation marks

* Fix issues

* Update Content.Shared/Maps/ContentTileDefinition.cs

Co-authored-by: metalgearsloth <31366439+metalgearsloth@users.noreply.github.com>

* Resolve some issues

* Remove unused method

* Fix more issues

* Fix more issues

* Fix more issues

* Fix more issues

* Fix issue, rollback SharedGhostComponent.cs

* Update submodule

* Fix issue, invert some if-statements to reduce nesting

* Revert RobustToolbox

* FIx things broken by merge

* Some fixes

- Replaced with string.Empty
- Remove some exclamation marks
- Revert file

* Some fixes

* Trivial #nullable enable

* Fix null ables

Co-authored-by: metalgearsloth <31366439+metalgearsloth@users.noreply.github.com>
Co-authored-by: Metal Gear Sloth <metalgearsloth@gmail.com>

Content.Shared/GameObjects/Components/PDA/SharedPDAComponent.cs

@@ -1,4 +1,5 @@
-using System;
+#nullable enable
+using System;
 using Robust.Shared.GameObjects;
 using Robust.Shared.Serialization;
 using Robust.Shared.ViewVariables;
@@ -51,8 +52,8 @@ namespace Content.Shared.GameObjects.Components.PDA
         public bool FlashlightEnabled;
         public bool HasPen;
         public PDAIdInfoText PDAOwnerInfo;
-        public UplinkAccountData Account;
-        public UplinkListingData[] Listings;
+        public UplinkAccountData Account = default!;
+        public UplinkListingData[] Listings = default!;
 
         public PDAUpdateState(bool isFlashlightOn, bool hasPen, PDAIdInfoText ownerInfo)
         {
@@ -107,9 +108,9 @@ namespace Content.Shared.GameObjects.Components.PDA
     [Serializable, NetSerializable]
     public struct PDAIdInfoText
     {
-        public string ActualOwnerName;
-        public string IdOwner;
-        public string JobTitle;
+        public string? ActualOwnerName;
+        public string? IdOwner;
+        public string? JobTitle;
     }
 
     [Serializable, NetSerializable]
@@ -127,7 +128,7 @@ namespace Content.Shared.GameObjects.Components.PDA
 
     public class UplinkAccount
     {
-        public event Action<UplinkAccount> BalanceChanged;
+        public event Action<UplinkAccount>? BalanceChanged;
         public EntityUid AccountHolder;
         private int _balance;
         [ViewVariables]
@@ -148,7 +149,6 @@ namespace Content.Shared.GameObjects.Components.PDA
             _balance = newBalance;
             BalanceChanged?.Invoke(this);
             return true;
-
         }
     }
 
@@ -185,7 +185,7 @@ namespace Content.Shared.GameObjects.Components.PDA
             ItemId = itemId;
         }
 
-        public bool Equals(UplinkListingData other)
+        public bool Equals(UplinkListingData? other)
         {
             if (other == null)
             {