Always return value when using TryGetValue. If Null, return empty rea…

…donly collection instead of null.

FastMoq.Core/Models/ConstructorHistory.cs

@@ -224,7 +224,7 @@ public bool Contains(Type key)
         public bool TryGetValue(Type key, out ReadOnlyCollection<IHistoryModel> value)
         {
             var result = constructorHistory.TryGetValue(key, out var value2);
-            value = value2?.AsReadOnly();
+            value = value2?.AsReadOnly() ?? new List<IHistoryModel>().AsReadOnly();
             return result;
         }