LOCK command is under-documented, fails on empty table

The LOCK command, mentioned in this blog post and this GS post, does not appear in the documentation. I would expect it to look something like the PostgreSQL documentation, including the discussion of lock types. Would love to see this updated.

It's especially important since I've found that calling LOCK on a newly created, empty table hangs. Nothing happens. It's not until there is at least one row that LOCK returns. Is there a way to LOCK an empty table? And if not, how do I tell if a table is empty so I don't try to lock it?