fix js -> php null judgement
fix js -> php null judgement

kkiernan/commonmark,bcremer/commonmark,kkiernan/commonmark,stof/commonmark,fesor/commonmark,fesor/commonmark,colinodell/commonmark,garethellis36/commonmark,thephpleague/commonmark,thephpleague/commonmark,postalservice14/commonmark,hason/commonmark,cebe/markdown-1,garethellis36/commonmark,postalservice14/commonmark,hason/commonmark