message: Fix null context construction
diff: @@ -418,7 +418,7 @@ class BatchNormalizationV2(Layer):
  # because of a bug which leads cond_v2 to skip rewriting them creating
  # conflicts.
  if tf2.enabled():
  - cm = contextlib.contextmanager(lambda: (yield))
  + cm = contextlib.contextmanager(lambda: (yield))()
  else:
  cm = ops.colocate_with(variable)
  with cm:
  