Linked Issue Field Behaviour.groovy

import com.adaptavist.hapi.jira.issues.Issues
import com.onresolve.jira.groovy.user.FieldBehaviours
import groovy.transform.BaseScript

@BaseScript FieldBehaviours behaviours
def linkedIssues = getFieldById('issuelinks-issues')
def linkedIssuesValue = linkedIssues.value as List<String>
linkedIssues.clearError()

linkedIssuesValue.each {
    def issue = Issues.getByKey(it)
    if (issue.issueType.name != 'Story') {
        linkedIssues.error = 'Only Story Types Are Allowed'
    }
}