I added a feature request to add a dedicated “END IF” node that would merge the TRUE and FALSE branches directly. I’d gladly work on this, if someone can give me a pointer - maybe another node (Merge?) that I could use as a starting point.
It’s counterintuitive but there is a workaround as mmac described above. You add an IF prior to your IF, set to always true, always send output. Then you feed that and the outcome of the ‘real’ IF to Merge, and set it to enhance the output from the always-true IF. Apparently, then the merge will continue, even if the real IF returns nothing.
Another solution is to put your IF into a sub-workflow with 2 outcome branches. This is what I’m doing - it’s cumbersome but it works.