Add items to an existing checklist

import com.onresolve.scriptrunner.runner.customisers.WithPlugin;
import com.atlassian.jira.component.ComponentAccessor;
import com.atlassian.jira.issue.MutableIssue;
@WithPlugin("com.okapya.jira.checklist")
import com.okapya.jira.customfields.*;

def ChecklistItem createChecklistItem(ChecklistCFType cfType, String name, boolean checked, String status, boolean mandatory, int rank) {
    def itemJson =  """
    {
        "name": "${name}",
        "checked": ${checked ? "true" : "false"},
        "statusId": "${status == null || status == "" ? "none" : status}",
        "mandatory": ${mandatory ? "true" : "false"},
        "rank": ${rank}
    }
    """;
    return cfType.getSingularObjectFromString(itemJson);
}

// Retrieve the Custom Field Type for the Checklist Custom Field
def customFieldManager = ComponentAccessor.getCustomFieldManager();
def checklistCustomField = customFieldManager.getCustomFieldObject("customfield_10013");
def checklistCustomFieldType = (ChecklistCFType) checklistCustomField.getCustomFieldType();

// Add items to the existing Checklist
def issue = (MutableIssue) event.issue;
def ArrayList<ChecklistItem> existingChecklistValue = (ArrayList<ChecklistItem>) issue.getCustomFieldValue(checklistCustomField);
def maxRank = existingChecklistValue.size();
existingChecklistValue.add( createChecklistItem(checklistCustomFieldType, "Move the folder structure", false, null, true, maxRank++) );
existingChecklistValue.add( createChecklistItem(checklistCustomFieldType, "Remove *.exe files", false, null, true, maxRank++) );

// Update the issue with the checklist
checklistCustomFieldType.updateValue(checklistCustomField, issue, existingChecklistValue);