Index: src/QtCore/QtChildEvent.h
==================================================================
--- src/QtCore/QtChildEvent.h
+++ src/QtCore/QtChildEvent.h
@@ -40,10 +40,13 @@
 namespace ObjQt {
 
 static OF_INLINE QtChildEvent *
 toOF(QChildEvent *qChildEvent)
 {
+	if (qChildEvent == NULL)
+		return nil;
+
 	return [[[QtChildEvent alloc]
 	    initWithQChildEvent: qChildEvent] autorelease];
 }
 
 static OF_INLINE QChildEvent *

Index: src/QtCore/QtCoreApplication.h
==================================================================
--- src/QtCore/QtCoreApplication.h
+++ src/QtCore/QtCoreApplication.h
@@ -43,10 +43,13 @@
 namespace ObjQt {
 
 static OF_INLINE QtCoreApplication *
 toOF(QCoreApplication *qCoreApplication)
 {
+	if (qCoreApplication == NULL)
+		return nil;
+
 	return [[[QtCoreApplication alloc]
 	    initWithQCoreApplication: qCoreApplication] autorelease];
 }
 
 static OF_INLINE QCoreApplication *

Index: src/QtCore/QtEvent.h
==================================================================
--- src/QtCore/QtEvent.h
+++ src/QtCore/QtEvent.h
@@ -47,10 +47,13 @@
 namespace ObjQt {
 
 static OF_INLINE QtEvent *
 toOF(QEvent *qEvent)
 {
+	if (qEvent == NULL)
+		return nil;
+
 	return [[[QtEvent alloc] initWithQEvent: qEvent] autorelease];
 }
 
 static OF_INLINE QEvent *
 toQt(QtEvent *event)

Index: src/QtCore/QtObject.h
==================================================================
--- src/QtCore/QtObject.h
+++ src/QtCore/QtObject.h
@@ -85,10 +85,13 @@
 namespace ObjQt {
 
 static OF_INLINE QtObject *
 toOF(QObject *qObject)
 {
+	if (qObject == NULL)
+		return nil;
+
 	return [[[QtObject alloc] initWithQObject: qObject] autorelease];
 }
 
 static OF_INLINE QObject *
 toQt(QtObject *object)

Index: src/QtCore/QtThread.h
==================================================================
--- src/QtCore/QtThread.h
+++ src/QtCore/QtThread.h
@@ -48,10 +48,13 @@
 namespace ObjQt {
 
 static OF_INLINE QtThread *
 toOF(QThread *qThread)
 {
+	if (qThread == NULL)
+		return nil;
+
 	return [[[QtThread alloc] initWithQThread: qThread] autorelease];
 }
 
 static OF_INLINE QThread *
 toQt(QtThread *thread)

Index: src/QtGui/QtGUIApplication.h
==================================================================
--- src/QtGui/QtGUIApplication.h
+++ src/QtGui/QtGUIApplication.h
@@ -49,10 +49,13 @@
 namespace ObjQt {
 
 static OF_INLINE QtGUIApplication *
 toOF(QGuiApplication *qGuiApplication)
 {
+	if (qGuiApplication == NULL)
+		return nil;
+
 	return [[[QtGUIApplication alloc]
 	    initWithQGuiApplication: qGuiApplication] autorelease];
 }
 
 static OF_INLINE QGuiApplication *

Index: src/QtWidgets/QtAbstractButton.h
==================================================================
--- src/QtWidgets/QtAbstractButton.h
+++ src/QtWidgets/QtAbstractButton.h
@@ -47,10 +47,13 @@
 namespace ObjQt {
 
 static OF_INLINE QtAbstractButton *
 toOF(QAbstractButton *qAbstractButton)
 {
+	if (qAbstractButton == NULL)
+		return nil;
+
 	return [[[QtAbstractButton alloc]
 	    initWithQAbstractButton: qAbstractButton] autorelease];
 }
 
 static OF_INLINE QAbstractButton *

Index: src/QtWidgets/QtAction.h
==================================================================
--- src/QtWidgets/QtAction.h
+++ src/QtWidgets/QtAction.h
@@ -69,10 +69,13 @@
 namespace ObjQt {
 
 static OF_INLINE QtAction *
 toOF(QAction *qAction)
 {
+	if (qAction == NULL)
+		return nil;
+
 	return [[[QtAction alloc] initWithQAction: qAction] autorelease];
 }
 
 static OF_INLINE QAction *
 toQt(QtAction *action)

Index: src/QtWidgets/QtApplication.h
==================================================================
--- src/QtWidgets/QtApplication.h
+++ src/QtWidgets/QtApplication.h
@@ -45,10 +45,13 @@
 namespace ObjQt {
 
 static OF_INLINE QtApplication *
 toOF(QApplication *qApplication)
 {
+	if (qApplication == NULL)
+		return nil;
+
 	return [[[QtApplication alloc]
 	    initWithQApplication: qApplication] autorelease];
 }
 
 static OF_INLINE QApplication *

Index: src/QtWidgets/QtPushButton.h
==================================================================
--- src/QtWidgets/QtPushButton.h
+++ src/QtWidgets/QtPushButton.h
@@ -43,10 +43,13 @@
 namespace ObjQt {
 
 static OF_INLINE QtPushButton *
 toOF(QPushButton *qPushButton)
 {
+	if (qPushButton == NULL)
+		return nil;
+
 	return [[[QtPushButton alloc]
 	    initWithQPushButton: qPushButton] autorelease];
 }
 
 static OF_INLINE QPushButton *

Index: src/QtWidgets/QtWidget.h
==================================================================
--- src/QtWidgets/QtWidget.h
+++ src/QtWidgets/QtWidget.h
@@ -227,10 +227,13 @@
 namespace ObjQt {
 
 static OF_INLINE QtWidget *
 toOF(QWidget *qWidget)
 {
+	if (qWidget == NULL)
+		return nil;
+
 	return [[[QtWidget alloc] initWithQWidget: qWidget] autorelease];
 }
 
 static OF_INLINE QWidget *
 toQt(QtWidget *widget)

Index: src/common/OFDataArray+QByteArray.h
==================================================================
--- src/common/OFDataArray+QByteArray.h
+++ src/common/OFDataArray+QByteArray.h
@@ -32,15 +32,21 @@
 namespace ObjQt {
 
 static OF_INLINE OFDataArray *
 toOF(const QByteArray &qByteArray)
 {
+	if (qByteArray.isNull())
+		return nil;
+
 	return [OFDataArray dataArrayWithQByteArray: qByteArray];
 }
 
 static OF_INLINE QByteArray
 toQt(OFDataArray *dataArray)
 {
+	if (dataArray == nil)
+		return QByteArray();
+
 	return [dataArray qByteArray];
 }
 
 }

Index: src/common/OFString+QString.h
==================================================================
--- src/common/OFString+QString.h
+++ src/common/OFString+QString.h
@@ -33,15 +33,21 @@
 namespace ObjQt {
 
 static OF_INLINE OFString *
 toOF(const QString &qString)
 {
+	if (qString.isNull())
+		return nil;
+
 	return [OFString stringWithQString: qString];
 }
 
 static OF_INLINE QString
 toQt(OFString *string)
 {
+	if (string == nil)
+		return QString();
+
 	return [string qString];
 }
 
 }

Index: src/common/helpers.h
==================================================================
--- src/common/helpers.h
+++ src/common/helpers.h
@@ -39,11 +39,11 @@
 {
 	return of_point(qPoint.x(), qPoint.y());
 }
 
 static OF_INLINE QPoint
-toQt(of_point_t point)
+toQt(const of_point_t &point)
 {
 	return QPoint(point.x, point.y);
 }
 
 static OF_INLINE of_dimension_t
@@ -51,11 +51,11 @@
 {
 	return of_dimension(qSize.width(), qSize.height());
 }
 
 static OF_INLINE QSize
-toQt(of_dimension_t dimension)
+toQt(const of_dimension_t &dimension)
 {
 	return QSize(dimension.width, dimension.height);
 }
 
 static OF_INLINE of_rectangle_t
@@ -64,12 +64,12 @@
 	return of_rectangle(qRect.x(), qRect.y(),
 	    qRect.width(), qRect.height());
 }
 
 static OF_INLINE QRect
-toQt(of_rectangle_t rectangle)
+toQt(const of_rectangle_t &rectangle)
 {
 	return QRect(rectangle.origin.x, rectangle.origin.y,
 	    rectangle.size.width, rectangle.size.height);
 }
 
 }