Fem: modernize C++11

* use nullptr

src/Mod/Fem/App/FemPostPipelinePyImp.cpp

@@ -45,19 +45,19 @@ PyObject* FemPostPipelinePy::read(PyObject *args)
         PyMem_Free(Name);
         Py_Return;
     }
-    return 0;
+    return nullptr;
 }
 
 PyObject* FemPostPipelinePy::load(PyObject *args)
 {
     PyObject* py;
     if (!PyArg_ParseTuple(args, "O!", &(App::DocumentObjectPy::Type), &py))
-        return 0;
+        return nullptr;
 
     App::DocumentObject* obj = static_cast<App::DocumentObjectPy*>(py)->getDocumentObjectPtr();
     if (!obj->getTypeId().isDerivedFrom(FemResultObject::getClassTypeId())) {
         PyErr_SetString(PyExc_TypeError, "object is not a result object");
-        return 0;
+        return nullptr;
     }
 
     getFemPostPipelinePtr()->load(static_cast<FemResultObject*>(obj));
@@ -67,7 +67,7 @@ PyObject* FemPostPipelinePy::load(PyObject *args)
 PyObject* FemPostPipelinePy::getLastPostObject(PyObject *args)
 {
     if (!PyArg_ParseTuple(args, ""))
-        return 0;
+        return nullptr;
 
     App::DocumentObject* obj = getFemPostPipelinePtr()->getLastPostObject();
     if (obj)
@@ -79,12 +79,12 @@ PyObject* FemPostPipelinePy::holdsPostObject(PyObject *args)
 {
     PyObject* py;
     if (!PyArg_ParseTuple(args, "O!", &(App::DocumentObjectPy::Type), &py))
-        return 0;
+        return nullptr;
 
     App::DocumentObject* obj = static_cast<App::DocumentObjectPy*>(py)->getDocumentObjectPtr();
     if (!obj->getTypeId().isDerivedFrom(FemPostObject::getClassTypeId())) {
         PyErr_SetString(PyExc_TypeError, "object is not a post-processing object");
-        return 0;
+        return nullptr;
     }
 
     bool ok = getFemPostPipelinePtr()->holdsPostObject(static_cast<FemPostObject*>(obj));
@@ -93,7 +93,7 @@ PyObject* FemPostPipelinePy::holdsPostObject(PyObject *args)
 
 PyObject *FemPostPipelinePy::getCustomAttributes(const char* /*attr*/) const
 {
-    return 0;
+    return nullptr;
 }
 
 int FemPostPipelinePy::setCustomAttributes(const char* /*attr*/, PyObject* /*obj*/)