gistfile1.php

<?php

//current way

$options = array(
  'key1' => 'value',
  'key2' => array(
    'key3' => ''
    )
);
add_option('option1', $options);

$opt = get_option('option1');
echo $opt['key4thatdoesntexist'] == 'doesnt exists error';


//new way

$options = array(
  'key1' => 'value',
  'key2' => array(
    'key3' => ''
    )
);
add_option('option2', $options);

function something($options){
  $defaults = array(
    'key1' => '',
    'key2' => array(
      'key3' => ''
      ),
    'key4thatdoesntexist' => ''
  );
  return recursive_array_function($options, $defaults);
}
add_filter('get_option_option2', 'something');

$opt = get_option('option2');//this is run through the above filter
echo $opt['key4thatdoesntexist'] == 'is part of the array because we added it in the filter (its empty, but it exists!)';