@Override
  public Object toJson(Object value) {
    if (value instanceof RelDistribution) {
      return toJson((RelDistribution) value);
    }
    if(value instanceof RelDataType) {
      return toJson((RelDataType) value);
    }
    return super.toJson(value);
  }
Hive extension of RelJson.
Implement json serialization of types which are not support by Calcite 1.21.0.
This class can be removed when Calcite is upgraded to 1.23.0
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/HiveRelJson.java