Create a New Fix Version of the Selected Project

import com.atlassian.jira.component.ComponentAccessor

// the key of the project under which the version will get created
final String projectKey = "JRA"

// the name of the version - required
final String versionName = "1.0.1"

// the start date - optional
final Date startDate = null

// the release date - optional
final Date releaseDate = null

// a description for the new version - optional
final String description = null

// id of the version to schedule after the given version object - optional
final Long scheduleAfterVersion = null

// true if this is a released version
final boolean released = false

def project = ComponentAccessor.projectManager.getProjectObjByKey(projectKey)
assert project : "Could not find project with key $projectKey"

ComponentAccessor.versionManager.createVersion(versionName, startDate, releaseDate, description, project.id, scheduleAfterVersion, released)