Validating a Checklist through scripting

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

// Retrieve the Custom Field Type for the Checklist Custom Field
def customFieldManager = ComponentAccessor.getCustomFieldManager();
def checklistCustomField = customFieldManager.getCustomFieldObject("customfield_10000");
def checklistCustomFieldType = (ChecklistCFType) checklistCustomField.getCustomFieldType();

// Add items to the existing Checklist
def ArrayList<ChecklistItem> existingChecklistValue = (ArrayList<ChecklistItem>) issue.getCustomFieldValue(checklistCustomField);

def anyItemChecked = false;
// Find out if any item is checked
for (ChecklistItem item : existingChecklistValue) {
    if (item.isChecked()) {
      anyItemChecked = true;
      break;
    }
}

if (!anyItemChecked) {
    throw new InvalidInputException("At least one item must be checked in '" + checklistCustomField.getName() + "' Checklist.");
}