def METHOD_NAME(self, obj: str) -> List[DimensionValue]:
    column_name = obj
    func = self._pyspark_func
    df = self._df.withColumn(
        column_name,
        func.when(
            func.col(column_name).isNull(), self._default_dimension_value
        ).otherwise(func.col(column_name)),
    )
    df_rdd = (
        df.withColumn(column_name, func.col(column_name).cast("string"))
        .select(column_name)
        .rdd
    )
    return df_rdd.flatMap(list).collect()