Make --allowlists optional

We don't always want to use an allowlist.

Test: m soong_generated_product_filesystem_test
Change-Id: I9e6ae7cdd488f8129fb97cd778ae9e9c77ec3cd2
diff --git a/tools/filelistdiff/file_list_diff.py b/tools/filelistdiff/file_list_diff.py
index fbbfedf..a6408e8 100644
--- a/tools/filelistdiff/file_list_diff.py
+++ b/tools/filelistdiff/file_list_diff.py
@@ -76,7 +76,7 @@
     parser.add_argument('kati_installed_file_list')
     parser.add_argument('soong_installed_file_list')
     parser.add_argument('system_module_name')
-    parser.add_argument('--allowlists', nargs='+')
+    parser.add_argument('--allowlists', nargs='*', default=[])
     args = parser.parse_args()
 
     find_unique_items(args.kati_installed_file_list, args.soong_installed_file_list, args.system_module_name, args.allowlists)
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