Crash when invoking blockBoundingRect over a QTextDocument documentLayout

#include <QAbstractTextDocumentLayout>
#include <QApplication>
#include <QDebug>
#include <QTextBlock>
#include <QTextDocument>

int main (int argc, char *argv[])
{
	QApplication a(argc, argv);
	QTextDocument d;
	QTextBlock b;
	if (d.documentLayout())
	{
		qDebug() << "Layout not null";
		d.documentLayout()->blockBoundingRect(b);
	}
}