Please use nullptr for a null pointer, not 0.

Please do not remove the override.

Also, our file format says that we should not have virtual and override in the same line. Any overridden method must be virtual implicitly.
That is because a virtual method in the base class is also virtual in the derived class. And override specifies that a method inside a derived class should override the same function inside the base class. To make this work, the method has to be virtual in the base class in the first place.