code: private int getInputLengthFromConfig(Map<String, Object> layerConfig) throws InvalidKerasConfigurationException {
          Map<String, Object> innerConfig = KerasLayerUtils.getInnerLayerConfigFromConfig(layerConfig, conf);
          if (!innerConfig.containsKey(conf.getLAYER_FIELD_INPUT_LENGTH()))
              throw new InvalidKerasConfigurationException(
                      "Keras Embedding layer config missing " + conf.getLAYER_FIELD_INPUT_LENGTH() + " field");
          if (innerConfig.get(conf.getLAYER_FIELD_INPUT_LENGTH()) == null) {
              return 0;
          } else {
              return (int) innerConfig.get(conf.getLAYER_FIELD_INPUT_LENGTH());
          }
      }
docs: Get Keras input length from Keras layer configuration. In Keras input_length, if present, denotes
  the number of indices to embed per mini-batch, i.e. input will be of shape (mb, input_length)
  and (mb, 1) else.
  
  @param layerConfig dictionary containing Keras layer configuration
  @return input length as int