code: def _get_optional_parameters(self):
      return {
          "lstm_units",
          "dropouts",
          "optim",
          "lr",
      } | super()._get_optional_parameters()
  
file_path: BigDL/python/chronos/src/bigdl/chronos/model/tf1/VanillaLSTM_keras.py
imports: from bigdl.orca.automl.model.base_keras_model import KerasBaseModel
  from collections.abc import Iterable
  import numpy
label_desc: Use image node_id 4 for calling the VanillaLSTM obj's underlying member method code with example usage: obj._get_optional_parameters() and returns: unknown