On ansible-core 2.19.0, invoking macro like this (which only outputted
something in its `if` block, not in `else`), resulted in a macro
outputting `None`.

One way to work around it is to add an explicit `else` block which also
outputs something.

A better way to work around it is to only invoke the macro if it
has something to output.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/4458