update: do not pass in user revspec as default destination (issue6044) When the revsingle() was introduced at 61c0df2b089a, it couldn't handle revspec=0 (not '0') properly. That's probably why the default was set to rev. This is technically BC since "hg update ''" was identical to "hg update '.'" whereas "hg update -r ''" is "hg update", but I believe that's a bug given no test fails with this change.

Set up

  $ hg init repo
  $ cd repo

Try to import an empty patch

  $ hg import --no-commit - <<EOF
  > EOF
  applying patch from stdin
  abort: stdin: no diffs found
  [255]

No dirstate backups are left behind

  $ ls .hg/dirstate* | sort
  .hg/dirstate