Merge branch 'f-is-reference-role' into 'dev'

F is reference role

See merge request !31

src/caosdb/common/models.py

@@ -1551,6 +1551,11 @@ class Property(Entity):
 
                 if server_retrieval:
                     tmp_prop = deepcopy(self)
+                    """
+                    remove role to avoid unnessecary ValueError while
+                    retrieving the Entity.
+                    """
+                    tmp_prop.role = None
                     tmp_prop.retrieve()
 
                     return tmp_prop.is_reference()