diff --git a/shopify_python/ast.py b/shopify_python/ast.py
index ea8f516..06a49ec 100644
--- a/shopify_python/ast.py
+++ b/shopify_python/ast.py
@@ -2,7 +2,7 @@
 
 
 def count_tree_size(node):  # type: (astroid.NodeNG) -> int
-    size = 1
+    size = 1 if node else 0
     for child in node.get_children():
         size += count_tree_size(child)
     return size