context: parents() already filters nullid

mercurial/context.py

@@ -439,7 +439,6 b' class filectx(object):'
         for f in sorted(visit, key=lambda x: x.rev()):
             curr = decorate(f.data(), f)
             for p in parents(f):
-                if p != nullid:
                     curr = pair(hist[p], curr)
                     # trim the history of unneeded revs
                     needed[p] -= 1