static Optional<FunctionReference> fromSerial(String serialForm) {
        Matcher expressionMatcher = referencePattern.matcher(serialForm);
        if ( ! expressionMatcher.matches()) return Optional.empty();

        String name = expressionMatcher.group(1);
        String instance = expressionMatcher.group(2);
        return Optional.of(new FunctionReference(name, instance));
    }
Returns a function reference from the given serial form, or empty if the string is not a valid reference
model-evaluation/src/main/java/ai/vespa/models/evaluation/FunctionReference.java