Added custom comparer to build TypeReference collections with

Editor/Util/SerializedTypeReference.cs

@@ -18,7 +18,7 @@ public SerializedTypeReference(SerializedProperty typeReferenceProperty)
         {
             _parentObject = typeReferenceProperty.serializedObject;
             _typeNameProperty = typeReferenceProperty.FindPropertyRelative(TypeReference.NameOfTypeNameField);
-            _guidProperty = typeReferenceProperty.FindPropertyRelative(TypeReference.NameOfGuidField);
+            _guidProperty = typeReferenceProperty.FindPropertyRelative(nameof(TypeReference.GUID));
             _guidAssignmentFailedProperty = typeReferenceProperty.FindPropertyRelative(nameof(TypeReference.GuidAssignmentFailed));
 
             SetGuidIfAssignmentFailed();

Runtime/TypeReference.cs

@@ -19,12 +19,11 @@ public sealed class TypeReference : ISerializationCallbackReceiver
         public const string NoneElement = "(None)";
 
         public const string NameOfTypeNameField = nameof(_typeNameAndAssembly);
-        public const string NameOfGuidField = nameof(_GUID);
 
         public bool GuidAssignmentFailed;
+        public string GUID;
 
         [SerializeField] private string _typeNameAndAssembly;
-        [SerializeField] private string _GUID;
         private Type _type;
 
         /// <summary>
@@ -79,7 +78,7 @@ public Type Type
 
         public static implicit operator Type(TypeReference typeReference)
         {
-            return typeReference.Type;
+            return typeReference?.Type;
         }
 
         public static implicit operator TypeReference(Type type)
@@ -100,13 +99,13 @@ private void SetClassGuidIfExists(Type type)
         {
             try
             {
-                _GUID = GetClassGUID(type);
+                GUID = GetClassGUID(type);
             }
             // It is thrown on assembly recompiling if field initialization is used on field.
             catch (UnityException)
             {
                 GuidAssignmentFailed = true;
-                _GUID = string.Empty;
+                GUID = string.Empty;
             }
         }
 

Runtime/TypeReferenceComparer.cs

@@ -0,0 +1,13 @@
+namespace TypeReferences
+{
+    using System.Collections.Generic;
+
+    /// <summary>Custom comparer that allows to build TypeReference collections.</summary>
+    public class TypeReferenceComparer : IEqualityComparer<TypeReference>
+    {
+        public bool Equals(TypeReference x, TypeReference y) => x?.Type == y?.Type;
+
+        public int GetHashCode(TypeReference obj) =>
+            string.IsNullOrEmpty(obj.GUID) ? obj.Type.GetHashCode() : obj.GUID.GetHashCode();
+    }
+}