OWASP Java HTML Sanitizer - rel attribute on a element

Question

I'm using the OWASP Java HTML Sanitizer to sanitize HTML input. The problem is that the "rel" attribute values "noopener" and "noreferrer" is duplicated or removed by the library.

I have an input like this: <a href="https://stackoverflow.com" rel="noopener noreferrer" target="_blank">StackOverflow</a> and I want that the safe HTML remains the same, because it's valid.

This is an example class to reproduce the problem:

import org.owasp.html.HtmlPolicyBuilder;
import org.owasp.html.PolicyFactory;

public class HtmlSanitizerError {

    public static void main(String[] args) {

        PolicyFactory policyFactory = new HtmlPolicyBuilder()
                .allowElements("a")
                .allowUrlProtocols("https")
                .skipRelsOnLinks("noopener", "noreferrer")   // with this line the "rel" attribute will be removed
                                                                        // without this line the "rel" attribute values will be duplicated 
                .allowAttributes("href", "rel", "target").onElements("a")
                .toFactory();

        String html = "<a href=\"https://stackoverflow.com\" rel=\"noopener noreferrer\" target=\"_blank\">StackOverflow</a>";

        String safeHTML = policyFactory.sanitize(html);

        System.out.println(safeHTML);
    }

}

I already see this similar issue on StackOverflow, but it didn't solve my problem: Java - Owasp Html Sanitizer shows double noopener noreferrer for url