Bug 1313426 - gecko decision task: ValueError: No JSON object. fix SETA. r=dustin

MozReview-Commit-ID: F4V3VcDHMnW

--HG--
extra : rebase_source : 2761f12b75f31701164d912c60be0f9d745ec883

taskcluster/taskgraph/util/seta.py

@@ -64,6 +64,10 @@ class SETA(object):
         except exceptions.RequestException as error:
             logger.warning(error)
 
+        # When we get invalid JSON (i.e. 500 error), it results in a ValueError (bug 1313426)
+        except ValueError as error:
+            logger.warning("Invalid JSON, possible server error: {}".format(error))
+
         return low_value_tasks
 
     def is_low_value_task(self, label, project):