log: remove any ancestors of nullrev (issue3772)

For the special case, ":null" we remove the implied revision 0 since that
wouldn't make any sense here. A test case is added to make sure only nullrev is
shown.

mercurial/scmutil.py

@@ -6,6 +6,7 b''
 # GNU General Public License version 2 or any later version.
 
 from i18n import _
+from mercurial.node import nullrev
 import util, error, osutil, revset, similar, encoding, phases
 import match as matchmod
 import os, errno, re, stat, sys, glob
@@ -647,6 +648,8 b' def revrange(repo, revs):'
                 start, end = spec.split(_revrangesep, 1)
                 start = revfix(repo, start, 0)
                 end = revfix(repo, end, len(repo) - 1)
+                if end == nullrev and start <= 0:
+                    start = nullrev
                 rangeiter = repo.changelog.revs(start, end)
                 if not seen and not l:
                     # by far the most common case: revs = ["-1:0"]

tests/test-log.t

@@ -1296,4 +1296,13 b' test hg log on non-existent files and on'
   changeset:   0:65624cd9070a
   $ hg log -l1 .d6/f1 | grep changeset
   changeset:   0:65624cd9070a
+
+issue3772: hg log -r :null showing revision 0 as well
+
+  $ hg log -r :null
+  changeset:   -1:000000000000
+  user:        
+  date:        Thu Jan 01 00:00:00 1970 +0000
+  
+
   $ cd ..