ValidateAddGroupToGroup.groovy

package examples.usermgr

import com.atlassian.jira.component.ComponentAccessor
import com.atlassian.jira.issue.Issue
import com.opensymphony.workflow.InvalidInputException

/* CONFIGURABLE SECTION */
def parentGroupFieldName = "Parent Group"
def childGroupFieldName = "Child Group"
/* END CONFIGURABLE SECTION */

def customFieldManager = ComponentAccessor.getCustomFieldManager()

Issue issue = issue

def customFields = customFieldManager.getCustomFieldObjects(issue)

[parentGroupFieldName, childGroupFieldName].each {fieldName ->
    def field = customFields.find { it.name == fieldName }
    assert field // fields not found or not associated with issue

    if (! issue.getCustomFieldValue(field)) {
        throw new InvalidInputException("Please enter both $parentGroupFieldName and $childGroupFieldName")
    }
}