[experiments] Test for job existance before cascading updates

beat/web/experiments/models.py

@@ -1058,6 +1058,7 @@ class Block(models.Model):
         '''
 
         for b in self.dependents.all():
+            if not hasattr(b, 'job'): continue
             if any([k.status in (Block.FAILED, Block.CANCELLED) \
                 for k in b.dependencies.all()]):
                 b.job._cancel()