I tried it but I do not know if that is correct.
function mytest() {
$value = get_field('my_options', 'option');
if ($value === NULL) {
$value = '1';
}
}
add_filter( 'acf/load_field/key=field_580b7d8b9ceea', 'mytest' );
$value = ‘1’ = true (from True/False field)?!
Unfortunately it does not work.