Mod: remove some more superfluous Boolean checks

src/Mod/Sketcher/App/SketchObject.cpp

@@ -7671,7 +7671,7 @@ std::string SketchObject::validateExpression(const App::ObjectIdentifier &path,
 {
     const App::Property * prop = path.getProperty();
 
-    assert(expr != nullptr);
+    assert(expr);
 
     if (!prop)
         return "Property not found";

src/Mod/Spreadsheet/App/PropertySheet.cpp

@@ -601,7 +601,7 @@ void PropertySheet::setStyle(CellAddress address, const std::set<std::string> &_
 void PropertySheet::setForeground(CellAddress address, const App::Color &color)
 {
     Cell * cell = nonNullCellAt(address);
-    assert(cell != nullptr);
+    assert(cell);
     cell->setForeground(color);
 }
 

src/Mod/Test/Gui/UnitTestImp.cpp

@@ -58,7 +58,7 @@ UnitTestDialog* UnitTestDialog::instance()
  */
 void UnitTestDialog::destruct ()
 {
-    if (_instance != nullptr) {
+    if (_instance) {
         UnitTestDialog *pTmp = _instance;
         _instance = nullptr;
         delete pTmp;