return Long instead of long, prevent possible null pointer if no trades for an asset
return Long instead of long, prevent possible null pointer if no trades for an asset

dmkaplan2000/nxt_dmk,Ziftr/nxt,fimkrypto/nxt,fimkrypto/nxt,duckx/nxt,metrospark/czarcraft,fimkrypto/nxt,duckx/nxt,dmkaplan2000/nxt_dmk,duckx/nxt,fimkrypto/nxt,Ziftr/nxt,dmkaplan2000/nxt_dmk,metrospark/czarcraft,Ziftr/nxt,metrospark/czarcraft