diff --git a/endpoints/trigger.py b/endpoints/trigger.py
index a0f945704..725b8aa1c 100644
--- a/endpoints/trigger.py
+++ b/endpoints/trigger.py
@@ -71,7 +71,7 @@ def _determine_build_ref(run_parameters, get_branch_sha, get_tag_sha, default_br
   kind = ''
   value = ''
 
-  if 'refs' in run_parameters:
+  if 'refs' in run_parameters and run_parameters['refs']:
     kind = run_parameters['refs']['kind']
     value = run_parameters['refs']['name']
   elif 'branch_name' in run_parameters: