Qt Assistant QMultiMap compiler errors

C:\dev\qt\dev\src\qttools\src\assistant\help\qhelpcollectionhandler.cpp(2360): error C2440: 'static_cast': cannot convert from 'QMap<QString,QUrl>' to 'QMultiMap<Key,T> &'
        with
        [
            Key=QString,
            T=QUrl
        ]
C:\dev\qt\dev\src\qttools\src\assistant\help\qhelpcollectionhandler.cpp(2360): note: static_cast and safe_cast to reference can only be used for valid initializations or for lvalue casts between related classes
C:\dev\qt\dev\src\qttools\src\assistant\help\qhelpcollectionhandler.cpp(2400): error C2440: 'static_cast': cannot convert from 'QMap<QString,QUrl>' to 'QMultiMap<Key,T> &'
        with
        [
            Key=QString,
            T=QUrl
        ]
C:\dev\qt\dev\src\qttools\src\assistant\help\qhelpcollectionhandler.cpp(2400): note: static_cast and safe_cast to reference can only be used for valid initializations or for lvalue casts between related classes
[