code: def to_json(self):
      self.save()
      data_json = {
          "new_features": self._new_features,
          "result_file": self._result_file,
          "input_columns": self._input_columns,
      }
      if self._error is not None and self._error:
          data_json["error"] = self._error
      return data_json
  
file_path: mljar-supervised/supervised/preprocessing/kmeans_transformer.py
imports: import datetime
  import json
  import os
  import time
  import joblib
  import numpy
  import pandas
  from sklearn.cluster import MiniBatchKMeans
  from sklearn.preprocessing import StandardScaler
  from supervised.exceptions import AutoMLException
label_desc: Use image node_id 5 for calling the KMeansTransformer obj's underlying member method code with example usage: obj.to_json() and returns: data_json