code: public static List<String> requiredColumns(String idColumnName) {
  
  		if (idColumnName == null) {
  			idColumnName = COLUMN_ID;
  		}
  
  		List<String> requiredColumns = new ArrayList<>();
  		requiredColumns.add(idColumnName);
  		requiredColumns.add(COLUMN_DATA);
  		requiredColumns.add(COLUMN_CONTENT_TYPE);
  		return requiredColumns;
  	}
docs: Get the required columns
  
  @param idColumnName
  id column name
  
  @return required columns