--- a/testing/mozharness/mozharness/mozilla/building/buildbase.py
+++ b/testing/mozharness/mozharness/mozilla/building/buildbase.py
@@ -2034,20 +2034,17 @@ or run without that action (ie: --no-{ac
 
         build_metrics = self._load_build_resources()
         if build_metrics:
             perfherder_data['suites'].append(build_metrics)
         perfherder_data['suites'].extend(self._load_sccache_stats())
 
         if self.query_is_nightly():
             for suite in perfherder_data['suites']:
-                if 'extraOptions' in suite:
-                    suite['extraOptions'] = ['nightly'] + suite['extraOptions']
-                else:
-                    suite['extraOptions'] = ['nightly']
+                suite.setdefault('extraOptions', []).insert(0, 'nightly')
 
         if perfherder_data["suites"]:
             self.info('PERFHERDER_DATA: %s' % json.dumps(perfherder_data))
 
     def sendchange(self):
         if os.environ.get('TASK_ID'):
             self.info("We are not running this in buildbot; skipping")
             return