According to Ben_Kelley from ATLASSIAN TEAM the currently used library

jira-rest-java-client is for server-edition of Jira only,

see https://community.atlassian.com/t5/Jira-questions/JIRA-REST-API-missing-parameters/qaq-p/1302944

Ben_Kelley ATLASSIAN TEAM Tuesday
Please note the section under "Compatibility with Jira" for JRJC on https://ecosystem.atlassian.net/wiki/spaces/JRJC/overview

The Jira REST Java Client works with Jira Server, but not with Jira Cloud.

When communicating with the cloud edition a self-generated (java) client should be used:

https://community.atlassian.com/t5/Jira-articles/Generating-a-REST-client-for-Jira-Cloud/ba-p/1307133

As the jenkins jira-plugin should work with cloud edition and onpremise server edition of Jira I guess there should be
a "generic api" 
above of the https://bitbucket.org/atlassian/jira-rest-java-client 
and the self-generated

encapsulating the core-jira-functions necessary for jira-plugin

to be sure all functions provided by jira-plugin work on both.

Current APIs:

Server Platform:

https://docs.atlassian.com/software/jira/docs/api/REST/8.7.1/

Cloud Platform: (v3 is already available as beta)

https://developer.atlassian.com/cloud/jira/platform/rest/v2/