Convention for leaving body of an if/else blank

Disclaimer

I'm not entirely sure if this is the right SE for this, but I'll start here anyway.

Background

I was reading this question earlier and was looking at this code snippet in one of the answers

auto z = [&](){ static auto cache_x = x; 
    static auto cache_y = y; 
    static auto cache_result = x + y;
    if (x == cache_x && y == cache_y)
       return cache_result;
    else
    {
        cache_x = x; 
        cache_y = y; 
        cache_result = x + y;
        return cache_result;
    }
};

Personally, I would be inclined to rewrite it as follows, with a single return statement

auto z = [&](){ static auto cache_x = x; 
    static auto cache_y = y; 
    static auto cache_result = x + y;
    if (x == cache_x && y == cache_y)
    {
    }
    else
    {
        cache_x = x; 
        cache_y = y; 
        cache_result = x + y;
    }
    return cache_result;
};

but this leaves a blank body for the if part.

We could rewrite the if/else to just be if(!(x == cache_x && y == cache_y)) but this runs the risk of being misunderstood (and can get messy).

My Question

What is the more accepted way of writing something like this, should we

• have multiple return statements
• leave the body of the if blank
• rewrite the if condition to be the negated version
• something else

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Please note, I usually code in Java whereas the sample code is in C++. I am interested in the generally accepted way of doing things, as opposed to specific C++ constructs/methods.