QPointer has an operator== overload for std::nullptr_t (a hidden friend, hence the somewhat weird prototype, but that seems irrelevant):

/*!
    \fn template <typename T> bool QPointer<T>::operator!=(std::nullptr_t, const QPointer<T> &rhs)
...

In the generated documentation, the function is documented as:

bool operator==(std::nullptr_t rhs, const QPointer<T> &)

Naming the first argument (e.g. "lhs") is a workaround, but then one has to document it as well to avoid qdoc warnings, whereas saying that "returns true when \a rhs is \nullptr" says everything there is to be said.