message: Fix cases where either predictions or eval_metric_ops is None.
diff: @@ -1684,9 +1684,11 @@ class _MultiHead(Head):
  for head, m in zip(self._heads, all_model_fn_ops):
  losses.append(m.loss)
  head_name = head.head_name
  - for k, v in m.predictions.items():
  + if m.predictions is not None:
  + for k, v in six.iteritems(m.predictions):
  predictions[(head_name, k)] = v
  - for k, v in m.eval_metric_ops.items():
  + if m.eval_metric_ops is not None:
  + for k, v in six.iteritems(m.eval_metric_ops):
  # metrics["%s/%s" % (k, head_name)] = v
  metrics[k] = v
  additional_train_ops.append(m.train_op)
  