fix: Empty user list for updating usergroup users sets usergroup as having no members

[rozza-sb]

Currently when an empty list is provided within UsergroupsUsersUpdateRequest, it is sent in the request as users=, which is not supported by the Slack API to denote a usergroup as having 0 members. This adds a case for checking an empty list, and using the accepted value of [] in the request if so.

Fixes #1573.

Category (place an x in each of the [ ])

• bolt (Bolt for Java)
• bolt-{sub modules} (Bolt for Java - optional modules)
• slack-api-client (Slack API Clients)
• slack-api-model (Slack API Data Models)
• slack-api-*-kotlin-extension (Kotlin Extensions for Slack API Clients)
• slack-app-backend (The primitive layer of Bolt for Java)

Requirements

Please read the Contributing guidelines and Code of Conduct before creating this issue or pull request. By submitting, you agree to those rules.

[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @rozza-sb to sign the Salesforce Inc. Contributor License Agreement.

[vegeris]

Thanks for updating this and adding tests!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.20%. Comparing base (d9e6798) to head (69a6dba).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1574      +/-   ##
============================================
+ Coverage     73.17%   73.20%   +0.03%     
- Complexity     4510     4514       +4     
============================================
  Files           477      477              
  Lines         14283    14285       +2     
  Branches       1487     1488       +1     
============================================
+ Hits          10451    10458       +7     
+ Misses         2939     2936       -3     
+ Partials        893      891       -2     

Flag	Coverage Δ
jdk-14	73.20% <100.00%> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.