App: modernize C++11

* use nullptr

src/App/GeoFeaturePyImp.cpp

@@ -40,13 +40,13 @@ std::string GeoFeaturePy::representation(void) const
 PyObject* GeoFeaturePy::getPaths(PyObject * /*args*/)
 {
     PyErr_SetString(PyExc_NotImplementedError, "Not yet implemented");
-    return 0;
+    return nullptr;
 }
 
 PyObject* GeoFeaturePy::getGlobalPlacement(PyObject * args) {
     
     if (!PyArg_ParseTuple(args, ""))
-        return 0;
+        return nullptr;
     
     try {
         Base::Placement p = static_cast<GeoFeature*>(getDocumentObjectPtr())->globalPlacement();
@@ -86,7 +86,7 @@ PyObject* GeoFeaturePy::getPropertyOfGeometry(PyObject * args)
 
 PyObject *GeoFeaturePy::getCustomAttributes(const char* /*attr*/) const
 {
-    return 0;
+    return nullptr;
 }
 
 int GeoFeaturePy::setCustomAttributes(const char* /*attr*/, PyObject* /*obj*/)