code: private Schema getCustomColumnSchema(String columnName) {
      Schema schema = new Schema();
      String dataType = "string";
      schema.setColumnName(columnName);
      String elementDataType = "string";
      List<String> mapSymbols = null;
      JsonObject newDataType = this.convertDataType(columnName, dataType, elementDataType, mapSymbols);
      schema.setDataType(newDataType);
      schema.setWaterMark(false);
      schema.setPrimaryKey(0);
      schema.setLength(0);
      schema.setPrecision(0);
      schema.setScale(0);
      schema.setNullable(true);
      schema.setFormat(null);
      schema.setComment("Custom column");
      schema.setDefaultValue(null);
      schema.setUnique(false);
      return schema;
    }
docs: Schema of a custom column - required if column not found in metadata
  
  @return column schema