checkout(
    [
        $class : 'GitSCM',
        branches : [[ name: "${branch}" ]],
        doGenerateSubmoduleConfigurations: false,
        extensions : [
            [$class : 'RelativeTargetDirectory',
             relativeTargetDir: targetDir
            ],
            [$class : 'CloneOption',
             reference: '/somefolder/repo'
            ]
        ],
        userRemoteConfigs : [[
            url : ssh://blahblah/some.git,
            credentialsId: ourCredentialsId
        ]]
    ]
)

[Pipeline] git
Fetching changes from the remote Git repository
 > git rev-parse --is-inside-work-tree # timeout=10
 > git config remote.origin.url ssh://blahblah/some.git # timeout=10
Fetching upstream changes from ssh://blahblah/some.git
 > git --version # timeout=10
using GIT_SSH to set credentials Bitb-ssh-read
 > git fetch --tags --progress ssh://blahblah/some.git +refs/heads/*:refs/remotes/origin/*
Checking out Revision 5eaf094e260b45a236792d8fd43f7d991bf9bbe0 (refs/remotes/origin/master)
 > git rev-parse refs/remotes/origin/master^{commit} # timeout=10
 > git rev-parse refs/remotes/origin/origin/master^{commit} # timeout=10
 > git config core.sparsecheckout # timeout=10
 > git checkout -f 5eaf094e260b45a236792d8fd43f7d991bf9bbe0
Commit message: "look mommy no hands"
First time build. Skipping changelog.

Using reference repository: /somefolder/repo