Specifying both --quality and --version options makes the caller's intent unclear since:

• If the user asks for build with a specific quality, the script determines the version for the given quality.
• If the user specifies a version, that means that s/he has already implicitly picked a quality since there is only ever one build with a given version number (with whatever quality it was built with).

Therefore, we have disallowed specifying both options within a single invocation with PR https://github.com/dotnet/website/pull/4088.
The commit fc0b11b introduced with #286 breaks the implementation in an unintended way.

I suggest that:

• We revert the commit.
• Clarify the error message since the current message can be interpreted as "at least one needs to be specified" rather than "at most one needs to be specified" (like it was done in this comment).
• Add some tests to make sure it works the intended way.