From 3ac32fa5f006a36a1a372f39d8fb2034227cf391 Mon Sep 17 00:00:00 2001
From: Erez Shinan <erezshin+git@gmail.com>
Date: Wed, 18 Jul 2018 16:00:42 +0300
Subject: [PATCH] Bug in PropagatePositions when supplying a reducing
 transformer

---
 lark/parse_tree_builder.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lark/parse_tree_builder.py b/lark/parse_tree_builder.py
index e3e14ee..b9a4158 100644
--- a/lark/parse_tree_builder.py
+++ b/lark/parse_tree_builder.py
@@ -27,7 +27,7 @@ class PropagatePositions:
     def __call__(self, children):
         res = self.node_builder(children)
 
-        if children:
+        if children and isinstance(res, Tree):
             for a in children:
                 if isinstance(a, Tree):
                     res.meta.line = a.meta.line