handle newer parser reduction behavior

uncompyle6/parsers/parse2.py

@@ -395,8 +395,8 @@ 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

uncompyle6/parsers/parse24.py

@@ -55,7 +55,7 @@ class Python24Parser(Python25Parser):
         invalid = super(Python24Parser,
                         self).reduce_is_invalid(rule, ast,
                                                 tokens, first, last)
-        if invalid:
+        if invalid or tokens is None:
             return invalid
 
         # FiXME: this code never gets called...

uncompyle6/parsers/parse26.py

@@ -258,7 +258,7 @@ class Python26Parser(Python2Parser):
         invalid = super(Python26Parser,
                         self).reduce_is_invalid(rule, ast,
                                                 tokens, first, last)
-        if invalid:
+        if invalid or tokens is None:
             return invalid
         if rule == ('and', ('expr', 'jmp_false', 'expr', '\\e_come_from_opt')):
             # Test that jmp_false jumps to the end of "and"