diff --git a/pylib/gyp/input.py b/pylib/gyp/input.py
index 6b61e4e2..7150269c 100644
--- a/pylib/gyp/input.py
+++ b/pylib/gyp/input.py
@@ -2536,6 +2536,8 @@ def ProcessListFiltersInDict(name, the_dict):
     lists = []
     del_lists = []
     for key, value in the_dict.items():
+        if not key:
+            continue
         operation = key[-1]
         if operation not in {"!", "/"}:
             continue