asMimeHeaderAttributeOrNull
Casts this RuleStringToEvaluate as a MimeHeaderAttribute and retrieves its kotlin.String value. Returns null if the RuleStringToEvaluate is not a MimeHeaderAttribute.
Casts this RuleStringToEvaluate as a MimeHeaderAttribute and retrieves its kotlin.String value. Returns null if the RuleStringToEvaluate is not a MimeHeaderAttribute.