Fix: Select Default Falsy

[liamduckett]

Hey, currently falsy default values do not function as expected for select inputs.

Consider the following example (included as a test):

$result = select(
    label: 'How many stars would you like to give?',
    options: ['3', '2', '1', '0'],
    default: '0',
);

I'd expect the highlighted option to be 0, but currently it is 3. This is because 0 is falsy - failing the if($this->default) check and resulting in the first option being highlighted by default.

My proposed fix for this, is to change the check to if($this->default !== null), allowing the following non-null falsy values to be used as defaults.

If this is merged, I'm happy to also look into other inputs that this may affect.

[liamduckett]

Static analysis failure doesn't look related?