Was trying to add in the multi-whatever pipeline to scan our github org's repos.

It just threw up with " Oops!
A problem occurred while processing the request
Logging ID=e96eb5fc-31ba-40ca-80e2-2a83e1fe6a92"

I had to go crawl through the server logs to find,

hudson.init.impl.InstallUncaughtExceptionHandler handleException
Caught unhandled exception with ID e96eb5fc-31ba-40ca-80e2-2a83e1fe6a92 java.lang.IllegalArgumentException: Repository URL must not be empty at PluginClassLoader for github-branch-source//org.jenkinsci.plugins.github_branch_source.GitHubRepositoryInfo.forRepositoryUrl(GitHubRepositoryInfo.java:83)

This should have been caught in the UI (form-missing-input) checks