[fix #182] require Set before calling Set.new in PropertySet
[fix #182] require Set before calling Set.new in PropertySet

joshsoftware/github,durai145/github,anabhilash619/github,yaoxiaoyong/github,samphilipd/github,davengeo/github,peter-murach/github,MalachiTatum/github,wicky-info/github,piotrmurach/github,firstval/github,cocktail-io/github,befairyliu/github