What does this overload mean?

Question

Can someone explain me what does this overload mean?

public static bool operator ==(Shop lhs, Shop rhs)
{
    if (Object.ReferenceEquals(lhs, null))
    {
        if (Object.ReferenceEquals(rhs, null))
        {
            return true;
        }
        return false;
    }

    return lhs.Equals(rhs);
}

I have never seen Object.ReferenceEquals in overload

Answer 1

This overload was intended to compare two instances of Shop. It uses Object.ReferenceEquals to determine if one of the instances is null.
It cannot use lhs == null or rhs == null, because this would again invoke the operator == and create an infinite recursion leading to a StackOverflowException.

If both instances are null it returns true (since they are equal).
If only one instance is null it returns false (since they are not equal).
If both instances are not null it returns the result of the Equals implementation of Shop.