Missing null check in ParseSortParameters

Description

Hi all,
When requesting using a query string with an empty sort segment, e.g.
/api/...?sort=
or
/api/...?sort=text,,number,
a 500 is thrown instead of gracefully handling the exception. This seems to be because there's a missing null check here.

I'd imagine that the intended behaviour should be to skip over this if block in the case that the sortSegment is null, however I could imagine that preventing empty sort segments at this point could also be beneficial.

Environment

• JsonApiDotNetCore Version: 3.1.0, 4.0.0-alpha3
• Other Relevant Package Versions:

[wisepotato]

Hi this will be fixed with the next alpha release