Handle new state events which don't have a common ancestor

synapse/state.py

@@ -179,6 +179,18 @@ class StateHandler(object):
                 key=lambda x: x.depth
             )
 
+            if not hasattr(missing_prev, "prev_state_id"):
+                # FIXME Hmm
+                # temporary fallback
+                for algo in conflict_res:
+                    new_res, curr_res = algo(new_branch, current_branch)
+
+                    if new_res < curr_res:
+                        defer.returnValue(False)
+                    elif new_res > curr_res:
+                        defer.returnValue(True)
+                return
+
             pdu_id = missing_prev.prev_state_id
             origin = missing_prev.prev_state_origin