Replace ORKNullAnswerValue test with more complete ORKIsAnswerEmpty.
Replace ORKNullAnswerValue test with more complete ORKIsAnswerEmpty.

jarrelscy/ResearchKit,weijentu/ResearchKit,YuanZhu-apple/ResearchKit,boland25/ResearchKit,md0u80c9/ResearchKit,jarrelscy/ResearchKit,chb/ResearchKit,cornelltech/ResearchKit,jimmyti/ResearchKit,oliverschaefer/ResearchKit,allen7wang/ResearchKit,shazino/ResearchKit,md0u80c9/ResearchKit,chb/ResearchKit,boland25/ResearchKit,weijentu/ResearchKit,chb/ResearchKit,umerkhan-apple/ResearchKit,jarrelscy/ResearchKit,KaiCode2/ResearchKit,cornelltech/ResearchKit,mluedke2/ResearchKit,oliverschaefer/ResearchKit,jeremiahyan/ResearchKit,YuanZhu-apple/ResearchKit,oliverschaefer/ResearchKit,mluedke2/ResearchKit,md0u80c9/ResearchKit,mluedke2/ResearchKit,umerkhan-apple/ResearchKit,boland25/ResearchKit,jeremiahyan/ResearchKit,YuanZhu-apple/ResearchKit,shazino/ResearchKit,YuanZhu-apple/ResearchKit,umerkhan-apple/ResearchKit,KaiCode2/ResearchKit,md0u80c9/ResearchKit,shazino/ResearchKit,jimmyti/ResearchKit,weijentu/ResearchKit,allen7wang/ResearchKit,oliverschaefer/ResearchKit,chb/ResearchKit,boland25/ResearchKit,KaiCode2/ResearchKit,jimmyti/ResearchKit,cornelltech/ResearchKit,jeremiahyan/ResearchKit,allen7wang/ResearchKit,weijentu/ResearchKit