[Nancy's Hamsters]

That looks male to me and if it was originally in with other males I have had foster males where the adult males in with the younger males actually castrated younger males in with them from large hording situations. It could also be a male who didn't develop correctly and the testicles didn't distend into the scrotal sack when a young pup. In dog terms he would be called cryptorchid and have no visible testicles