Make use of Q_NULLPTR.

src/core/Metadata.h

@@ -24,6 +24,7 @@
 #include <QtGui/QColor>
 #include <QtGui/QImage>
 
+#include "core/Global.h"
 #include "core/Uuid.h"
 
 class Database;
@@ -34,7 +35,7 @@ class Metadata : public QObject
     Q_OBJECT
 
 public:
-    explicit Metadata(QObject* parent = 0);
+    explicit Metadata(QObject* parent = Q_NULLPTR);
 
     QString generator() const;
     QString name() const;