updates to swagger-parser 2.0.28

[benzvan]

Updates swagger parser to mitigate vulnerability in dependent httpclient library.
#10818

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package 
  ./bin/generate-samples.sh
  ./bin/utils/export_docs_generators.sh
  

  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  For Windows users, please run the script in Git BASH.
• File the PR against the correct branch: master (5.3.0), 6.0.x
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

[benzvan]

I believe the build failure to be transient network issues but don't have permission to re-run it.

[wing328]

@benzvan thanks for the PR. Is this a regression? Did the changelog mention anything related to this change?

[benzvan]

That must have crept in when I ran the generator scripts. I didn't notice any output related to it.

[benzvan]

Though reading it maybe it's just being more explicit? Seems like it's reasonable for a nullableWithNullDefault to have a default of null

[benzvan]

I'm not familiar enough with the upstream project to speak intelligently to the change though. I just know it used to use a 4-year-old version of httpclient. :-D

[benzvan]

@wing328 any followup thoughts? The only line I manually changed was the version number for swagger-parser.

[benzvan]

Poking around the swagger-parser notes I see this could be related but I don't know enough about the code to be sure.
https://github.com/swagger-api/swagger-parser/pull/1600/files

[wing328]

@benzvan thanks again for the PR. I've filed #11388 to upgrade to 2.0.29 instead so closing this one.