handle anonymous gists
handle anonymous gists

user field is None for anonymous gists
christophelec/nbviewer,franblas/beaker-sharing-server,bollwyvl/nbviewer,twosigma/beaker-sharing-server,Jay-Oh-eN/nbviewer,thomasyu888/nbviewer,AlfiyaZi/nbviewer,twosigma/beaker-sharing-server,iamjakob/nbviewer,Jay-Oh-eN/nbviewer,AlfiyaZi/nbviewer,christophelec/nbviewer,bollwyvl/nbviewer,franblas/beaker-sharing-server,franblas/beaker-sharing-server,roxyboy/nbviewer,franblas/beaker-sharing-server,thomasyu888/nbviewer,imsparsh/nbviewer,twosigma/beaker-sharing-server,Sage-Bionetworks/nbviewer,roxyboy/nbviewer,Sage-Bionetworks/nbviewer,imsparsh/nbviewer,twosigma/beaker-sharing-server,iamjakob/nbviewer