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/Network/NetMessages/MsgUpdateAdminStatus.cs

@@ -1,4 +1,6 @@
-using Content.Shared.Administration;
+#nullable enable
+using System;
+using Content.Shared.Administration;
 using Lidgren.Network;
 using Robust.Shared.Network;
 
@@ -15,8 +17,8 @@ namespace Content.Shared.Network.NetMessages
 
         #endregion
 
-        public AdminData Admin;
-        public string[] AvailableCommands;
+        public AdminData? Admin;
+        public string[] AvailableCommands = Array.Empty<string>();
 
         public override void ReadFromBuffer(NetIncomingMessage buffer)
         {
@@ -55,16 +57,14 @@ namespace Content.Shared.Network.NetMessages
                 buffer.Write(cmd);
             }
 
-            var isAdmin = Admin != null;
-            buffer.Write(isAdmin);
+            buffer.Write(Admin != null);
 
-            if (isAdmin)
-            {
-                buffer.Write(Admin.Active);
-                buffer.WritePadBits();
-                buffer.Write((uint) Admin.Flags);
-                buffer.Write(Admin.Title);
-            }
+            if (Admin == null) return;
+
+            buffer.Write(Admin.Active);
+            buffer.WritePadBits();
+            buffer.Write((uint) Admin.Flags);
+            buffer.Write(Admin.Title);
         }
 
         public override NetDeliveryMethod DeliveryMethod => NetDeliveryMethod.ReliableOrdered;