I have this in my code. It is almost perfect except there is a row of NULL width and a column of NULL substance in it. How do I get rid of them? Any idea?

#DEFINE THISGRID THISFORM.cappsumgrid1

SELECT STR(Roll_wdth.roll_wdth,5), Substance.substance,;
SUM(IIF(INLIST(Pa_trans.trans_type,"I","S"),-Pa_trans.roll_wgt,Pa_trans.roll_wgt));
FROM pbcs!substance FULL JOIN pbcs!pa_trans;
FULL JOIN pbcs!roll_wdth ;
ON Roll_wdth.roll_wdth = Pa_trans.roll_wdth ;
ON Substance.substance = Pa_trans.substance;
GROUP BY Roll_wdth.roll_wdth, Substance.substance;
ORDER BY Roll_wdth.roll_wdth, Substance.substance;
INTO CURSOR SYS(2015)
DO (_GENXTAB) WITH 'pachart_tbl',.F.,.T.,.T.,,,,.T.