Merge pull request #103 from realitycollective/feature/fix-system-typ…

…e-filter

Fix NRE with Implements attribute when no exclude types set

Editor/PropertyDrawers/TypeReferencePropertyDrawer.cs

@@ -163,7 +163,7 @@ where type.IsVisible && isValid
                             where (FilterConstraintOverride == null || FilterConstraintOverride.Invoke(type)) &&
                                   (filter == null || filter.IsConstraintSatisfied(type))
                             where excludedTypes == null || !excludedTypes.Contains(type)
-                            where !type.GetInterfaces().Any(interfaceType => excludedTypes.Contains(interfaceType))
+                            where !type.GetInterfaces().Any(interfaceType => excludedTypes != null && excludedTypes.Contains(interfaceType))
                             select type);
         }