Fix warnings and code cleanup/fixes (#13570)

Content.Server/Atmos/EntitySystems/AtmosphereSystem.Gases.cs

@@ -17,7 +17,7 @@ namespace Content.Server.Atmos.EntitySystems
         /// <summary>
         ///     List of gas reactions ordered by priority.
         /// </summary>
-        public IEnumerable<GasReactionPrototype> GasReactions => _gasReactions!;
+        public IEnumerable<GasReactionPrototype> GasReactions => _gasReactions;
 
         /// <summary>
         ///     Cached array of gas specific heats.

Content.Server/Atmos/EntitySystems/AtmosphereSystem.HighPressureDelta.cs

@@ -125,7 +125,7 @@ namespace Content.Server.Atmos.EntitySystems
                 // We step through tiles according to the pressure direction on the current tile.
                 // The goal is to get a general direction of the airflow in the area.
                 // 3 is the magic number - enough to go around corners, but not U-turns.
-                var curTile = tile!;
+                var curTile = tile;
                 for (var i = 0; i < 3; i++)
                 {
                     if (curTile.PressureDirection == AtmosDirection.Invalid

Content.Server/Atmos/EntitySystems/AtmosphereSystem.Processing.cs

@@ -51,7 +51,7 @@ namespace Content.Server.Atmos.EntitySystems
             if (!TryComp(uid, out MapGridComponent? mapGridComp))
                 return true;
 
-            var mapUid = _mapManager.GetMapEntityIdOrThrow(Transform(((Component) mapGridComp).Owner).MapID);
+            var mapUid = _mapManager.GetMapEntityIdOrThrow(Transform(mapGridComp.Owner).MapID);
 
             var volume = GetVolumeForTiles(mapGridComp, 1);
 

Content.Server/Atmos/Miasma/AntiRottingContainerComponent.cs

@@ -1,9 +1,9 @@
 namespace Content.Server.Atmos.Miasma
 {
-    [RegisterComponent]
     /// <summary>
     /// Entities inside this container will not rot.
     /// </summary>
+    [RegisterComponent]
     public sealed class AntiRottingContainerComponent : Component
     {}
 }

Content.Server/Atmos/Miasma/BodyPreservedComponent.cs

@@ -1,9 +1,9 @@
 namespace Content.Server.Atmos.Miasma
 {
-    [RegisterComponent]
     /// <summary>
     /// Way for natural sources of rotting to tell if there are more unnatural preservation forces at play.
     /// </summary>
+    [RegisterComponent]
     public sealed class BodyPreservedComponent : Component
     {
         public int PreservationSources = 0;

Content.Server/Atmos/Miasma/PerishableComponent.cs

@@ -2,11 +2,11 @@ using Robust.Shared.Serialization.TypeSerializers.Implementations.Custom;
 
 namespace Content.Server.Atmos.Miasma
 {
-    [RegisterComponent]
     /// <summary>
     /// This makes mobs eventually start rotting when they die.
     /// It may be expanded to food at some point, but it's just for mobs right now.
     /// </summary>
+    [RegisterComponent]
     public sealed class PerishableComponent : Component
     {
         /// <summary>

Content.Server/Atmos/Piping/Unary/Components/GasVentScrubberComponent.cs

@@ -78,7 +78,7 @@ namespace Content.Server.Atmos.Piping.Unary.Components
             if (!data.FilterGases.SequenceEqual(FilterGases))
             {
                 FilterGases.Clear();
-                foreach (var gas in data.FilterGases!)
+                foreach (var gas in data.FilterGases)
                     FilterGases.Add(gas);
             }
         }

Content.Server/Atmos/Piping/Unary/EntitySystems/GasPortableSystem.cs

@@ -59,7 +59,7 @@ namespace Content.Server.Atmos.Piping.Unary.EntitySystems
 
             foreach (var entityUid in grid.GetLocal(coordinates))
             {
-                if (EntityManager.TryGetComponent<GasPortComponent>(entityUid, out port))
+                if (EntityManager.TryGetComponent(entityUid, out port))
                 {
                     return true;
                 }

Content.Server/Atmos/Reactions/GasReactionPrototype.cs

@@ -21,7 +21,7 @@ namespace Content.Server.Atmos.Reactions
     public sealed class GasReactionPrototype : IPrototype
     {
         [ViewVariables]
-        [IdDataFieldAttribute]
+        [IdDataField]
         public string ID { get; } = default!;
 
         /// <summary>