localrepo: recognize trivial "null" queries in `anyrev`

Bypassing the revset logic for trivial "null" queries means we can avoid to
trigger the filtering logic in some cases.

Differential Revision: https://phab.mercurial-scm.org/D7481

mercurial/localrepo.py

@@ -1652,6 +1652,8 b' class localrepository(object):'
         definitions overriding user aliases, set ``localalias`` to
         ``{name: definitionstring}``.
         '''
+        if specs == [b'null']:
+            return revset.baseset([nullrev])
         if user:
             m = revset.matchany(
                 self.ui,

tests/test-repo-filters-tiptoe.t

@@ -49,5 +49,4 b' Getting the node of `null`'
   $ hg init test-repo
   $ cd test-repo
   $ hg log -r null -T "{node}\n"
-  debug.filters: computing revision filter for "visible"
   0000000000000000000000000000000000000000