Just FYI, there is a pull request on the git-client-plugin in preparation for this: https://github.com/jenkinsci/git-client-plugin/pull/279
There is also a corresponding change in the git-plugin that uses it: https://github.com/ansig/git-plugin/commit/7e6de1ee3c9c2e7442cc4b59e61fd4ce01073ff8
Would be good to see this fixed.