diff --git a/tools/gn2bp/gen_android_bp b/tools/gn2bp/gen_android_bp
index b4942e6..9031290 100755
--- a/tools/gn2bp/gen_android_bp
+++ b/tools/gn2bp/gen_android_bp
@@ -338,7 +338,7 @@
     self.local_include_dirs = set()
     self.header_libs = set()
     self.required = set()
-    self.tool_files = None
+    self.tool_files = []
     self.android = Target('android')
     self.host = Target('host')
     self.stl = None