Yes, there are dogs that are pretty much all German show line bloodlines who are solid black. I'm about 95% sure that these dogs have the dominant black gene.
The dominant black gene was deliberately eliminated (or mostly eliminated) from the GSD breed to help preserve the sable and saddle/black-tan color and pattern. The gene for solid black is in a different location (K locus) than the genes for sable/saddle/recessive black (agouti locus) and it "overrules" whatever agouti information the dog may carry. So a dominant black dog only needs to have 1 gene for black present to produce solid black puppies from any GSD it is mated with. It is also possible for a dog to have the dominant black gene and to have the recessive black gene.
Although these solid black conformation dogs are generally quite attractive, the question is: What are we going to do if the dominant black gene becomes common again in the breed?
Nowadays, it is possible to test for the dominant black gene--I think people would start demanding DNA tests on any black dog.
A dog with the dominant black color -- you don't know what sort of mask or what color their tan is; do they have the gene for the fading saddle? Well if you breed that black dog and some of the puppies are solid black and the rest have no mask or almost no saddle, you're SOL if you wanted to show those black/tan puppies. We all have seen the desire to have strongly pigmented black-red dogs--this dominant black gene hides that pattern, so you don't know what you're breeding. And unlike the recessive black gene that generally extends the coverage of the black areas on a sable or saddle patterned dog, the dominant black gene doesn't have any effect as far as improving the pigment of any puppies that do not inherit the dominant black gene (that is, the pups will either be solid black or will have no effect whatsoever from the parent's dominant black gene--because if they aren't black, they didn't get the gene).
Hope that makes some sense!