Error applying PUM23

While applying PUM23 to a 9.2 database and PT 8.55.14, I receive an error on the "Run Data Conversion AE-DCAP2494162" step where the SQL is trying to update a field to NULL:

UPDATE PS_VCHR_LINE_WTHD SET PS_VCHR_LINE_WTHD.WTHD_RULE = ( SELECT B.WTHD_RULE FROM PS_PYMNT_VCHR_WTHD B WHERE B.BUSINESS_UNIT = PS_VCHR_LINE_WTHD.BUSINESS_UNIT AND B.VOUCHER_ID = PS_VCHR_LINE_WTHD.VOUCHER_ID AND B.WTHD_ENTITY = PS_VCHR_LINE_WTHD.WTHD_ENTITY AND B.WTHD_TYPE = PS_VCHR_LINE_WTHD.WTHD_TYPE AND B.WTHD_JUR_CD = PS_VCHR_LINE_WTHD.WTHD_JUR_CD AND B.WTHD_CLASS = PS_VCHR_LINE_WTHD.WTHD_CLASS AND B.PYMNT_CNT = ( SELECT MAX(BB.PYMNT_CNT) FROM PS_PYMNT_VCHR_WTHD BB WHERE BB.BUSINESS_UNIT = B.BUSINESS_UNIT AND BB.VOUCHER_ID = B.VOUCHER_ID ) ) WHERE PS_VCHR_LINE_WTHD.WTHD_RULE = ' ' AND EXISTS ( SELECT 'X' FROM PS_PYMNT_VCHR_WTHD W WHERE W.BUSINESS_UNIT = PS_VCHR_LINE_WTHD.BUSINESS_UNIT AND W.VOUCHER_ID = PS_VCHR_LINE_WTHD.VOUCHER_ID )