I think this has only started since upgrading to 0.8.81. It definitely worked at one point previously.
I used to be able to pull just the :db/id, e.g. to find the id from my own :db/unique attribute:
(db/pull db [:db/id] [:foo/id my-id])
That now fails with
com.google.common.util.concurrent.UncheckedExecutionException: Syntax error compiling
As a workaround I can just use
[*]. Is such a pattern not allowed, or is this a bug?