Accept a list when deserialising a UnionRef

Author: szymonlopaciuk

xobjects/ref.py

@@ -183,7 +183,7 @@ def _to_buffer(cls, buffer, offset, value, info=None):
         else:
             if value is None:
                 xobj = None
-            elif isinstance(value, tuple):
+            elif isinstance(value, (tuple, list)):  # accept list as it might be coming from JSON
                 if len(value) == 0:
                     xobj = None
                     typeid = None