Validate the Organizations field

import com.onresolve.jira.groovy.user.FieldBehaviours
import groovy.json.JsonSlurper
import groovy.transform.BaseScript

@BaseScript FieldBehaviours behaviours
def organization = getFieldById(fieldChanged)
def organizationValue = organization.formValue as List
organization.clearError()

//Specify the Service Desk's ID
final def serviceDeskId = '<SERVICE_DESK_ID>'
final def host = applicationProperties.getString('jira.baseurl')
final def restEndpointName = 'getOrganizations'

def baseUrl = "${host}/rest/scriptrunner/latest/custom/${restEndpointName}?serviceDeskId=${serviceDeskId}"
def response = baseUrl.toURL().text

def json = new JsonSlurper().parseText(response) as Map

organizationValue.each {
    def output = json[it].toString()
    //Validate characters used in the String
    if (!Character.isLetter(output.charAt(0)) || !Character.isLetter(output.charAt(1)) || !Character.isDigit(output.charAt(2))
            || !Character.isDigit(output.charAt(3)) || !Character.isDigit(output.charAt(4)) || output.charAt(5).toString() != '_') {
        organization.setError("Invalid Characters Used")
    }
}