Core commit by Niall: Avoid fatal error if a UrlHandler isn't available
Core commit by Niall: Avoid fatal error if a UrlHandler isn't available

RhubarbPHP/Rhubarb,robertfalconer/Rhubarb,acuthbert/rhubarb,robertfalconer/Rhubarb,RhubarbPHP/Rhubarb,acuthbert/rhubarb