--- a/mozharness/mozilla/building/buildbase.py
+++ b/mozharness/mozilla/building/buildbase.py
@@ -839,24 +839,28 @@ or run without that action (ie: --no-{ac
     def _query_who(self):
         """ looks for who triggered the build with a change.
 
         This is used for things like try builds where the upload dir is
         associated with who pushed to try. First it will look in self.config
         and failing that, will poll buildbot_config
         If nothing is found, it will default to returning "nobody@example.com"
         """
-        _who = ''
+        _who = "nobody@example.com"
         if self.config.get('who'):
             _who = self.config['who']
-        if self.buildbot_config and 'sourcestamp' in self.buildbot_config:
-            if self.buildbot_config['sourcestamp'].get('who'):
-                _who = self.buildbot_config['sourcestamp']['who']
-        if not _who:
-            _who = "nobody@example.com"
+        else:
+            try:
+                if self.buildbot_config:
+                    _who = self.buildbot_config['sourcestamp']['changes'][0]['who']
+            except (KeyError, IndexError):
+                # KeyError: "sourcestamp" or "changes" or "who" not in buildbot_config
+                # IndexError: buildbot_config['sourcestamp']['changes'] is empty
+                # "who" is not available, using the default value
+                pass
         return _who
 
     def _query_post_upload_cmd(self):
         c = self.config
         post_upload_cmd = ["post_upload.py"]
         buildid = self.query_buildid()
         revision = self.query_revision()
         platform = self.stage_platform