C++ returning default value, NullObjectPattern

I have a question regarding some kind of Null Object Pattern. When I think of a getter (I know that we should avoid that but suppose) I see 2 ways of doing that.

Suppose that we have a class NullObject.cpp

1)

class NullObject
{
    std::vector<SomeObject> get() { return {}; }
}

class SomeImplementation
{
     std::vector<SomeObject> get() { return someVectorMember; }
{

const std::vector<SomeObject>& object = instance.get();

So in first example we will always returning by value and assign to const Object&

2)

class NullObject
{
    const std::vector<SomeObject>& get() { return member; }

    static std::vector<SomeObject> member;
}

class SomeImplementation
{
     const std::vector<SomeObject>& get() { return someVectorMember; }
{

const std::vector<SomeObject>& object = instance.get();

In this case we have static member in Null class so we can return a const reference.

Question: Which is better in case of performance for example? Which is better in case of "clean" code? Is there any (better) option? Maybe my example are wrong?

Thanks