A link to Special:Mute was added in T218270. However, as @dom_walden points out in T218270#5351777 the link is still visable even if there are not mute options available. This results in the error message:
Mute features are unavailable. This might be because: you haven't confirmed your email address or the wiki administrator has disabled email features and/or email blacklist for this wiki.
This is a bad user experience. The link should not be shown if there's nothing the user can do. This is the equivalent to showing links the user does not have access to.
Override SpecialPage::userCanExecute() in SpecialMute and ensure that a user has "access" to execute the page. Then ensure that this method is being called before the link is displayed.
We will also need to overrided SpecialPage::checkPermissions() to ensure that the same error is shown (i.e. not an access denied error).