JiraVersionParameterValue doesn't implement getValue(). The parent class has a getValue() that always returns null. As a result, using a JiraVersionParameterDefinition for input always results in a null value.

Here was the equivalent fix in 2015 for JiraIssueParameterValue: https://github.com/jenkinsci/jira-plugin/commit/0100428a5528e7aefd99a1800cedd66441547110

In the below example, approval.version is always null. However, approval.approver is set correctly.

def input_params = [[ $class: 'JiraVersionParameterDefinition', name: 'version', description: 'Version to be assigned', jiraProjectKey: 'TWEN',
jiraShowReleased: 'false', jiraShowArchived: 'false' ]]

def approval = input id: 'release-po-approval', message: 'Approve the release?', ok: 'Approve', parameters: input_params, submitterParameter: 'approver'