Blank archive_command

Hi,

Should archive_command being blank when archiving is enabled result in
a fatal error? This doesn't even produce a warning when restarting,
just an entry in the log when it goes to archive a WAL segment, and
finds the archive_command is empty.

Is there a valid scenario where someone would have archiving enabled
but no archive command? Naturally it will build up WAL until it is
corrected, which will result in a less desirable error, and likely at
a less convenient time, and to avoid it, someone either has to have
checked the logs and noticed this error, or got curious as to why
their WAL collection is nearly running out of shelf space.

Thom