I’m not so clear on the question, but if you want to a solution to use another channel if one is empty here is one way: How can I assign a default channel to another channel if it’s empty, while retaining its original content when it’s not empty, considering the default value is also a channel? - #3 by mahesh.binzerpanchal
Edit: Ah, now I got it. Yes, your solution to use a sentinel value is correct. There’s some examples in the Nextflow Slack if you search for Sentinel.