message: AggregatingVariable.initializer should be a property not a method.
diff: @@ -1560,8 +1560,9 @@ class AggregatingVariable(variables_lib.Variable):
  assign_fn = lambda var, *a, **kw: var.assign(*a, **kw)
  return self._assign_func(f=assign_fn, *args, **kwargs)
  + @property
  def initializer(self):
  - return self._v.initializer()
  + return self._v.initializer
  def eval(self, session=None):
  return self._v.eval(session)
  