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.

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Set up

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  $ hg init repo

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  $ cd repo

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Try to import an empty patch

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  $ hg import --no-commit - <<EOF

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  > EOF

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  applying patch from stdin

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  abort: stdin: no diffs found

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  [255]

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No dirstate backups are left behind

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  $ ls .hg/dirstate* | sort

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  .hg/dirstate

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