QString can be compared with NULL if (and only if) QT_NO_CAST_TO_ASCII/QT_NO_CAST_FROM_ASCII is set

As reproducible with the following example, which should not compile. It does not compile when QT_NO_CAST_FROM_ASCII/QT_NO_CAST_TO_ASCII are not set.

#define QT_NO_CAST_FROM_ASCII
#define QT_NO_CAST_TO_ASCII

#include <QtCore/QString>


int main(int argc, char* argv[])
{
    QString q;
    bool b = q == NULL;
    return 0;
}

NULL gets implicitly converted into a QStringRef, which then executes the following comparison operator:

bool operator==(const QString &s1,const QStringRef &s2)

It might be possible to fix this by making the following c'tor explicit:

inline QStringRef::QStringRef(const QString *aString)
    :m_string(aString), m_position(0), m_size(aString?aString->size() : 0){}