response body json raw errod data - Ajax wont accept json when array

I have the following line of code:

          print json_encode($organization_modules);

$organization_modules is an array that looks like this:

When i print this array to the following Ajax:

   $.ajax({
    type: 'POST',
    url: '/Module/findByCategory',
    dataType: 'json',
    data: {
        request: 'ajax',
        category_id: id
    },
    success: function (data) {
        $('#module_content').html('');
        $('#module_content').prepend('<div class="col-md-12"><a href="/Modules/index" class="btn btn-primary"><i class="fa fa-arrow-left"></i> Tilbage</a></div>');
        if(data.length > 0)
        {});

Nothing happens
However if i print the following instead:

it works just fine?
So does it have something to do with the null values or what is going on?
Response body

    <br />
<font size='1'><table class='xdebug-error xe-notice' dir='ltr' border='1' cellspacing='0' cellpadding='1'>
<tr><th align='left' bgcolor='#f57900' colspan="5"><span style='background-color: #cc0000; color: #fce94f; font-size: x-large;'>( ! )</span> Notice: Undefined offset: 0 in C:\xampp\htdocs\learning-bank\site\pages\models\Module.php on line <i>43</i></th></tr>
<tr><th align='left' bgcolor='#e9b96e' colspan='5'>Call Stack</th></tr>
<tr><th align='center' bgcolor='#eeeeec'>#</th><th align='left' bgcolor='#eeeeec'>Time</th><th align='left' bgcolor='#eeeeec'>Memory</th><th align='left' bgcolor='#eeeeec'>Function</th><th align='left' bgcolor='#eeeeec'>Location</th></tr>
<tr><td bgcolor='#eeeeec' align='center'>1</td><td bgcolor='#eeeeec' align='center'>0.0290</td><td bgcolor='#eeeeec' align='right'>141200</td><td bgcolor='#eeeeec'>{main}(  )</td><td title='C:\xampp\htdocs\learning-bank\index.php' bgcolor='#eeeeec'>..\index.php<b>:</b>0</td></tr>
<tr><td bgcolor='#eeeeec' align='center'>2</td><td bgcolor='#eeeeec' align='center'>0.0930</td><td bgcolor='#eeeeec' align='right'>202464</td><td bgcolor='#eeeeec'>Framework\Core\Classes\PageRenderer->__construct(  )</td><td title='C:\xampp\htdocs\learning-bank\index.php' bgcolor='#eeeeec'>..\index.php<b>:</b>14</td></tr>
<tr><td bgcolor='#eeeeec' align='center'>3</td><td bgcolor='#eeeeec' align='center'>0.0980</td><td bgcolor='#eeeeec' align='right'>254256</td><td bgcolor='#eeeeec'>Framework\Core\Classes\PageRenderer->executeAjax(  )</td><td title='C:\xampp\htdocs\learning-bank\core\classes\PageRenderer.php' bgcolor='#eeeeec'>..\PageRenderer.php<b>:</b>55</td></tr>
<tr><td bgcolor='#eeeeec' align='center'>4</td><td bgcolor='#eeeeec' align='center'>0.1010</td><td bgcolor='#eeeeec' align='right'>324752</td><td bgcolor='#eeeeec'>Module->findByCategory(  )</td><td title='C:\xampp\htdocs\learning-bank\core\classes\PageRenderer.php' bgcolor='#eeeeec'>..\PageRenderer.php<b>:</b>302</td></tr>
</table></font>
[{"id":"1","Category_id":"1","name":"Adf\u00e6rds styring","description":"Hello world","price":"200","mentor":null,"location":null,"start_date":null,"end_date":null,"time":null,"is_online":"1","status_id":"1","Material_id":null,"is_owned":"false"}]

Fixed it
I fixed it, apprently php was breaking because of undefined index

•   You have an PHP errors in your response, try to switch off warnings in PHP. In the begginning of the file add:

  error_reporting( 0 );  
  ini_set( "display_errors", "0" );  
  

  And thet you can get valid json.
  Or try to fix this notice on 14 line in index.php.