Fix Notifier.listeners_for

If no Trie.find returns None, then node.data will return an
AttributeError.

flake8/plugins/notifier.py

@@ -31,7 +31,8 @@ class Notifier(object):
         path = error_code
         while path:
             node = self.listeners.find(path)
-            for listener in node.data:
+            listeners = getattr(node, 'data', [])
+            for listener in listeners:
                 yield listener
             path = path[:-1]
 

tests/unit/test_notifier.py

@@ -38,3 +38,17 @@ class TestNotifier(object):
         self.notifier.notify('E111', 'extra', 'args')
         assert self.listener_map['E111'].was_notified is True
         assert self.listener_map['E1'].was_notified is True
+
+    @pytest.mark.parametrize('code', ['W123', 'W12', 'W1', 'W'])
+    def test_no_listeners_for(self, code):
+        """Show that we return an empty list of listeners."""
+        assert list(self.notifier.listeners_for(code)) == []
+
+    @pytest.mark.parametrize('code,expected', [
+        ('E101', ['E101', 'E1']),
+        ('E211', ['E211', 'E2']),
+    ])
+    def test_listeners_for(self, code, expected):
+        """Verify that we retrieve the correct listeners."""
+        assert ([l.error_code for l in self.notifier.listeners_for(code)] ==
+                expected)