ligaSub with ZWJ?

Hi! I’d like to replace “ct” by a ct-ligature only if there is a ZWJ between “c” and “t”, how can I write this in the ligaSub table?
Something like this obviously doesn’t work :unamused:

lookup ligaSub {
sub c ZWJ t -> ct;
}

After a long night I finally came to get it working, sorry for the false alarm.