public Optional<String> getSelectorLabel() {
        return Optional.ofNullable(selectorLabel);
    }
Gets the token that is used in {@link Selector} expressions when
referring to the relationship or an empty {@code Optional} if this
relationship is not used directly in a selector.

@return Returns the optionally present selector token for this relationship.
smithy-model/src/main/java/software/amazon/smithy/model/neighbor/RelationshipType.java