Fix AudioParams deserialization (#3191)

Robust.Shared/Audio/AudioParams.cs

@@ -82,7 +82,7 @@ namespace Robust.Shared.Audio
         ///     If not null, this will randomly modify the pitch scale by adding a number drawn from a normal distribution with this deviation.
         /// </summary>
         [DataField("variation")]
-        public float? Variation { get; set; }
+        public float? Variation { get; set; } = null;
 
         // For the max distance value: it's 2000 in Godot, but I assume that's PIXELS due to the 2D positioning,
         // so that's divided by 32 (EyeManager.PIXELSPERMETER).
@@ -91,6 +91,9 @@ namespace Robust.Shared.Audio
         /// </summary>
         public static readonly AudioParams Default = new(0, 1, "Master", SharedAudioSystem.DefaultSoundRange, 1, 1, false, 0f);
 
+        // explicit parameterless constructor required so that default values get set properly.
+        public AudioParams() { }
+
         public AudioParams(
             float volume,
             float pitchScale,

Robust.Shared/Containers/ContainerManagerComponent.cs

@@ -222,7 +222,10 @@ namespace Robust.Shared.Containers
         {
             [DataField("entities")] public List<EntityUid> Entities = new ();
 
-            [DataField("type")] public string? Type;
+            [DataField("type")] public string? Type = null;
+
+            // explicit parameterless constructor is required.
+            public ContainerPrototypeData() { }
 
             public ContainerPrototypeData(List<EntityUid> entities, string type)
             {