Validate prototype ids in c# fields (#18224)

Content.Shared/Body/Prototypes/BodyPrototype.cs

@@ -34,6 +34,10 @@ public sealed record BodyPrototypeSlot
     public readonly HashSet<string> Connections = new();
     public readonly Dictionary<string, string> Organs = new();
 
+    public BodyPrototypeSlot() : this(null, null, null)
+    {
+    }
+
     public BodyPrototypeSlot(string? part, HashSet<string>? connections, Dictionary<string, string>? organs)
     {
         Part = part;