Something something tokens something tokens
The below line seems to now be a problem for contribution receipts when using Order api. Trying to track it down - a (non-core) unit test that was working before is failing.
Based on the lines above it, filter is expected to possibly be null, so
$filter errors. That seems pretty clear regardless.
What's confusing me is there must be tests in core that would trigger this, basically anything that uses order api + payment to complete a contribution, so am looking closer.