Duplication

1. Go to an agent's script console (http://<jenkins>/computer/<agent node>/script)
2. Run this script

   import org.jenkinsci.plugins.p4.workspace.StreamWorkspaceImpl;
   import org.jenkinsci.plugins.p4.groovy.P4Groovy;
   
   def ws = new StreamWorkspaceImpl('none', false, '//Stream_Depot/Main', 'job1-temp-branch1')
   def p4 = new P4Groovy('credential', null, ws, new FilePath(new File('workspace')))
   def result = p4.run('status')

   Error: 'java.lang.IllegalStateException: Jenkins.instance is missing. Read the documentation of Jenkins.getInstanceOrNull to see what you are doing wrong.'

Can also be duplicated by running the following script in a Jenkinsfile

def ws = [$class: 'StreamWorkspaceImpl', charset: 'none', format: env.JOB_NAME + '-temp-' + env.BRANCH_NAME, pinHost: false, streamName: '//Stream_Depot/' + env.BRANCH_NAME] def p4 = p4(credential: 'credential', workspace: ws) def result = p4.run('streams')

Expected Result

I can use P4Groovy on an agent with no errors.

Workaround

Run P4Groovy commands in a separate stage running on the master. If data is needed, use Environment Variables to transfer variables to agent.