The "test-phantoms" command:

Usage: fossil test-phantoms

Show all phantom artifacts. A phantom artifact is one for which there is no content. Options:

--count

Show only a count of the number of phantoms.

--delta

Show all delta-phantoms. A delta-phantom is a artifact for which there is a delta but the delta source is a phantom.

--list

Just list the phantoms. Do not try to describe them.