add nil testing for miner
add nil testing for miner

rivine/rivine,mnsl/Sia,ericflo/Sia,mharkus/Sia,rivine/rivine,mharkus/Sia,mtlynch/Sia,johnathanhowell/Sia,mnsl/Sia,ericflo/Sia,Mingling94/Sia,NebulousLabs/Sia,ChrisSchinnerl/Sia,ChrisSchinnerl/Sia,mtlynch/Sia,MrStrong/Sia,NebulousLabs/Sia,MrStrong/Sia