import groovy.transform.BaseScript
import com.onresolve.jira.groovy.user.FieldBehaviours
@BaseScript FieldBehaviours fieldBehaviours
final String screenName = 'Some Screen Name'
final String fieldName = 'Some Field Name'
final String expectedValue = 'Some Value'
if (fieldScreen.name == screenName) {
def field = getFieldByName(fieldName)
field.value == expectedValue ? field.clearError() : field.setError('This is not a valid value')
}