Why not just skip empty tags?
With swagger2markup.pathsGroupedBy=TAGS the evaluation fails if there are no tags due to
https://github.com/Swagger2Markup/swagger2markup/blob/8e22dd817e5d4bef276894c0d5975d3c7254253d/src/main/java/io/github/swagger2markup/internal/document/PathsDocument.java#L121
I would argue that a hard failure is inappropriate here. Why not just log a warning and group by AS_IS (the default) instead?
To signal that the user made a mistake and forgot to provide tags. If he wants to group by tags, he must provide tags.
Now that we can process entire folders of Swagger files the case is slightly different I'd argue. I basically want to say "Group by tags if tags are available". Smaller service contracts in that folder may not have (and not need) tags.
Would you like to provide a PR? Automatic fallback to AS_IS and output a warning.
I meet the same problem and solved it with reflection.Maybe Setting the tag to some value is a solution.