Return UDT from Pandas UDF: @pandas_udf(UDT)

class BoxType(UserDefinedType):
    @classmethod
    def sqlType(cls) -> StructType:
        return StructType(
            fields=[
                StructField("xmin", DoubleType(), False),
                StructField("ymin", DoubleType(), False),
                StructField("xmax", DoubleType(), False),
                StructField("ymax", DoubleType(), False),
            ]
        )

@pandas_udf(
     returnType=StructType([StructField("boxes", ArrayType(Box()))]
)
def pandas_pf(s: pd.DataFrame) -> pd.DataFrame:
       yield s

try:
                to_arrow_type(self._returnType_placeholder)
            except TypeError:
>               raise NotImplementedError(
                    "Invalid return type with scalar Pandas UDFs: %s is "
E                   NotImplementedError: Invalid return type with scalar Pandas UDFs: StructType(List(StructField(boxes,ArrayType(Box,true),true))) is not supported