diff --git a/convlab/util/multiwoz/lexicalize.py b/convlab/util/multiwoz/lexicalize.py
index 1e5f7ce69eb046e391d752533d024cf9b766ff66..8fd794a3aa6fd7fe641c94fec6d7ea3ee6e99c60 100755
--- a/convlab/util/multiwoz/lexicalize.py
+++ b/convlab/util/multiwoz/lexicalize.py
@@ -87,7 +87,7 @@ def lexicalize_da(meta, entities, state, requestable):
                             pair[1] = entities[domain][n][slot.capitalize()]
                         elif slot_old in entities[domain][n]:
                             pair[1] = entities[domain][n][slot_old]
-                        elif slot in state[domain]:
+                        elif state.get(domain) is not None and slot in state.get(domain):
                             pair[1] = state[domain][slot]
                         else:
                             pair[1] = 'not available'