Ignore builders without result

Tools/Scripts/webkitpy/tool/commands/rebaseline.py

Index: Tools/Scripts/webkitpy/tool/commands/rebaseline.py
diff --git a/Tools/Scripts/webkitpy/tool/commands/rebaseline.py b/Tools/Scripts/webkitpy/tool/commands/rebaseline.py
index bb2ff336a08e989de7bd44c0a59240dded076ede..8564e686b1cdb7612095bc20a2a65c5ce4e6dd55 100644
--- a/Tools/Scripts/webkitpy/tool/commands/rebaseline.py
+++ b/Tools/Scripts/webkitpy/tool/commands/rebaseline.py
@@ -323,7 +323,11 @@ class AbstractParallelRebaselineCommand(AbstractRebaseliningCommand):
         if not self._builder_data:
             for builder_name in self._release_builders():
                 builder = self._tool.buildbot.builder_with_name(builder_name)
-                self._builder_data[builder_name] = builder.latest_layout_test_results()
+                builder_results = builder.latest_layout_test_results()
+                if builder_results:
+                    self._builder_data[builder_name] = builder_results
+                else:
+                    _log.warning("No result for builder '%s'" % builder_name)
         return self._builder_data
 
     # The release builders cycle much faster than the debug ones and cover all the platforms.