Avoid "No outputs found matching patterns" when output is deliberately not created

[wjchulme]

Suppose I have an action (an R script, say) that returns a file only if some property of the data is met. In that case, if ever that condition is not met, then running this action results in an error No outputs found matching patterns: output/not-always-produced.txt

Is there a way to side-step this error so that the action completes successfully?

[wjchulme]

A couple of workarounds that will work for now:

a) Have the script create a dummy output file whenever that condition is not met, or always create the dummy file and have it overwritten whenever the condition is met.
b) Use catch-all pattern-matching so that as long as some files match the pattern, the error won't occur, for example output/*.txt