If I don't specify a particular branch name, using JGit integration, I get
an error.

Workaround is to specify one.

Building remotely on jenkins-1 in workspace /jenkins/workspace/Realtime-dev-main
Fetching changes from the remote Git repository
Checking out Revision 6dff8ca0de2e9605c295d09106b756485dbbe22d (origin/dev/main)
FATAL: Could not checkout null
hudson.plugins.git.GitException: Could not checkout null
at org.jenkinsci.plugins.gitclient.JGitAPIImpl.checkout(JGitAPIImpl.java:200)
at org.jenkinsci.plugins.gitclient.JGitAPIImpl.checkoutBranch(JGitAPIImpl.java:231)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at hudson.remoting.RemoteInvocationHandler$RPCRequest.perform(RemoteInvocationHandler.java:299)
at hudson.remoting.RemoteInvocationHandler$RPCRequest.call(RemoteInvocationHandler.java:280)
at hudson.remoting.RemoteInvocationHandler$RPCRequest.call(RemoteInvocationHandler.java:239)
at hudson.remoting.UserRequest.perform(UserRequest.java:118)
at hudson.remoting.UserRequest.perform(UserRequest.java:48)
at hudson.remoting.Request$2.run(Request.java:326)
at hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:72)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
Caused by: org.eclipse.jgit.api.errors.InvalidRefNameException: Branch name <null> is not allowed
at org.eclipse.jgit.api.CheckoutCommand.processOptions(CheckoutCommand.java:471)
at org.eclipse.jgit.api.CheckoutCommand.call(CheckoutCommand.java:200)
at org.jenkinsci.plugins.gitclient.JGitAPIImpl.checkout(JGitAPIImpl.java:185)
... 17 more