remove NaN in categories checking (#20372)
remove NaN in categories checking (#20372)


rs2/pandas,GuessWhoSamFoo/pandas,jreback/pandas,pratapvardhan/pandas,louispotok/pandas,cython-testbed/pandas,gfyoung/pandas,amolkahat/pandas,jorisvandenbossche/pandas,kdebrab/pandas,harisbal/pandas,cython-testbed/pandas,dsm054/pandas,kdebrab/pandas,harisbal/pandas,amolkahat/pandas,cbertinato/pandas,gfyoung/pandas,TomAugspurger/pandas,jreback/pandas,MJuddBooth/pandas,datapythonista/pandas,dsm054/pandas,jreback/pandas,gfyoung/pandas,rs2/pandas,MJuddBooth/pandas,gfyoung/pandas,cython-testbed/pandas,amolkahat/pandas,TomAugspurger/pandas,dsm054/pandas,cbertinato/pandas,pandas-dev/pandas,TomAugspurger/pandas,louispotok/pandas,datapythonista/pandas,louispotok/pandas,toobaz/pandas,cbertinato/pandas,pratapvardhan/pandas,louispotok/pandas,toobaz/pandas,MJuddBooth/pandas,pratapvardhan/pandas,harisbal/pandas,GuessWhoSamFoo/pandas,dsm054/pandas,kdebrab/pandas,pandas-dev/pandas,amolkahat/pandas,jorisvandenbossche/pandas,MJuddBooth/pandas,TomAugspurger/pandas,toobaz/pandas,gfyoung/pandas,pratapvardhan/pandas,harisbal/pandas,dsm054/pandas,pandas-dev/pandas,kdebrab/pandas,pandas-dev/pandas,jorisvandenbossche/pandas,pratapvardhan/pandas,cbertinato/pandas,cython-testbed/pandas,datapythonista/pandas,GuessWhoSamFoo/pandas,amolkahat/pandas,harisbal/pandas,toobaz/pandas,rs2/pandas,toobaz/pandas,cbertinato/pandas,jorisvandenbossche/pandas,MJuddBooth/pandas,jreback/pandas,kdebrab/pandas,cython-testbed/pandas,GuessWhoSamFoo/pandas,datapythonista/pandas,rs2/pandas,louispotok/pandas,jreback/pandas,GuessWhoSamFoo/pandas