Unable to save settings of GHPRB

[PavelCZE]

Version report

Jenkins and plugins versions report:

Jenkins: 2.277.1
ghprb:1.42.2

Reproduction steps

• Create a new Freestyle project (or go to settings of exiting one)
• Set GitHub Pull Request Builder to true (or every job that is already using ghpbr)
• Save

Results

Expected result:

Project is saved

Actual result:

Project saving fails with error message:
JSONObject["org-jenkinsci-plugins-ghprb-GhprbTrigger"] is not a JSONObject.

Log shows the following incorrect JSON structure

"org-jenkinsci-plugins-ghprb-GhprbTrigger":true,"gitHubAuthId":"abc-abc-abc-abc-abc","adminlist":"","useGitHubHooks":false,"triggerPhrase":"","onlyTriggerPhrase":false,"autoCloseFailedPullRequests":false,"skipBuildPhrase":".*\\[skip\\W+ci\\].*","displayBuildErrorsOnDownstreamBuilds":false,"cron":["H/5 * * * *","H/5 * * * *",""],"whitelist":"","orgslist":"","blackListLabels":"","whiteListLabels":"","allowMembersOfWhitelistedOrgsAsAdmin":false,"permitAll":false,"buildDescTemplate":"","blackListCommitAuthor":"","whiteListTargetBranches":{"branch":""},"blackListTargetBranches":{"branch":""},"includedRegions":"","excludedRegions":"",