Fix a None issue

jedi/api/completion.py

@@ -343,6 +343,7 @@ class Completion:
         if stack_node.nonterminal == 'funcdef':
             context = get_user_context(self._module_context, self._position)
             node = search_ancestor(leaf, 'error_node', 'funcdef')
+            if node is not None:
                 if node.type == 'error_node':
                     n = node.children[0]
                     if n.type == 'decorators':