detectLinks may pass invalid URLs to javadoc(1)

The url of artifact com.sun.mail:mailapi:1.5.5 is http://javamail.java.net/mailapi, so the plugin tests if http://javamail.java.net/mailapi/apidocs/package-list is valid.
That url redirects to https://javaee.github.io/javamail/ which is JavaMail home page, so the plugin thinks the url is valid and passes it to javadoc.
javadoc warns about invalid link.

Maybe checking if the effective url is still "package-list" would be safer.