Question

I also get confused how to check if a variable is false/null when returned from a function.

When to use empty() and when to use isset() to check the condition ?

Answer 1

For returns from functions, you use neither isset nor empty, since those only work on variables and are simply there to test for possibly non-existing variables without triggering errors.

For function returns checking for the existence of variables is pointless, so just do:

if (!my_function()) {
    // function returned a falsey value
}

To read about this in more detail, see The Definitive Guide To PHP’s isset And empty.