handle None for tissue input data
handle None for tissue input data

zsloan/genenetwork2,genenetwork/genenetwork2,genenetwork/genenetwork2,pjotrp/genenetwork2,pjotrp/genenetwork2,pjotrp/genenetwork2,pjotrp/genenetwork2,zsloan/genenetwork2,genenetwork/genenetwork2,zsloan/genenetwork2,zsloan/genenetwork2,pjotrp/genenetwork2,genenetwork/genenetwork2