Recently, we haven't updated the Jenkins version and its plugin version also. My all source codes are maintaining in GitLab. When i create a new branch in Gitlab for a repository, new branch Jenkins job was not created in Jenkins server due to the indexing for the multi-branch pipeline is not triggered (not working). 

When i triggered the push event hook in my GitLab repository, i got 500 server error in GitLab.

What is the issue? How can i resolve this?

Any help would be much appreciated. If you need any details, please let me know.