handle newer parser reduction behavior

uncompyle6/parsers/parse2.py

@@ -397,8 +397,8 @@ class Python2Parser(PythonParser):
         return
 
     def reduce_is_invalid(self, rule, ast, tokens, first, last):
-        if not tokens:
-            return
+        if tokens is None:
+            return False
         lhs = rule[0]
         if lhs in ('augassign1', 'augassign2') and ast[0][0] == 'and':
             return True