JFactory::getApplication()->input->post->get() prunes empty sub arrays/objects

Question

I am sending a POST ajax call like this:

var request = {
    option    : 'com_ajax',
    module    : 'mod_test',  // to target: mod_test
    method    : 'Test',  // to target: function TestAjax in class modTestHelper
    format    : 'raw',
    data      : {a: [], b: {}, c: [0], d: [null]}
};
$.ajax({method: 'POST', data: request})
// .success( ...yatta yatta

I am receiving with:

$data = JFactory::getApplication()->input->post->get('data', array(), 'array');

However, the passed empty subarray (a) and subobject (b) are purged before reaching my php script. So, the contents of $data is ['c'=>'0', 'd'=>['']]. In other words, when I call isset($data['a']) or isset($data['b']) they evaluate as false.

For my module, I ended up passing the string 0 to represent an empty array, but my code would be tidier if I was permitted to pass an empty array to php. (For my project, the first level has a known number of elements, only the subarrays are dynamically generated.)

1. Is this a bug, a feature, and/or a known behavior?
2. Am I able to adjust my JFactory... line to accept empty subarrays?

I did get some insight but not a complete solution from these related answers:

• https://joomla.stackexchange.com/a/4233/12352
• https://joomla.stackexchange.com/a/5344/12352
• https://joomla.stackexchange.com/a/17659/12352
• https://joomla.stackexchange.com/a/4558/12352

I am using Joomla 3.8.6

Answer 1

If you dumped the $_POST in your helper's ajax method you would see that those empty arrays don't hit the server. Joomla's input object is entirely dependent on retrieving the values from $_POST.

JQuery ajax doesn't pass empty arrays, see this for example further reading: https://stackoverflow.com/questions/9397669/jquery-ajax-jsonp-how-to-actually-send-an-array-even-if-its-empty