Can't submit input name array to show up in Entry List

I figured it out.

Let's say I have
<input type="number" name="input_2[]" />

I would use the gform_pre_submission hook to convert the input array to a json string

add_action("gform_pre_submission_1", "pre_submission_handler");
function pre_submission_handler($form){
   $_POST["input_2"] = json_encode($_POST["input_2"]);
}

Then if I want to render the json string as a list on the Entry detail page I would use the gform_entry_field_value hook like so

add_filter("gform_entry_field_value", "category_names", 10, 4);
function category_names($value, $field, $lead, $form){

	if($form['id'] != 1 || $field['id'] != 2)
		return $value;

	$newvalue = '';
    $choices = json_decode($value, true);

    foreach($choices as $choice) {
        $new_value .= '<li>'.$choice.'</li>';
    }

    return '<ul>' . $new_value . '</ul>';
}

The only issue I have now is that the email notification returns the json string. Is there anyway to format the values before the email notification is sent?

I'm trying to do exactly the same thing but getting "null" value in return. My input fields look like:

<input name="field_4[]" type="text" value="Add note...">

and I'm otherwise basically using wlcx code, just replacing 2 with 4. My full code is at the pastebin link below:

http://pastebin.com/xRDNmGk3

The field I'm editing is a a Single Line Text with ID of 4. Any help would be super appreciated.

Thanks Chris, the code is in functions.php, and "null" shows up in the Entries page, under the column heading "Shopping List", which is the input I am modifying (ID#4, CSS .subsection). On the front-end, my complete HTML looks like this:

<li id="field_1_4" class="gfield    subsection">

<label class="gfield_label" for="input_1_4">Shopping List</label><br>

<label for="fav5454">CTC Analytics / Leap Technologies CombiPAL Headspace Autosampler</label><input style="width: 98%" name="field_4[]" id="fav5454" type="text" value="Add question..."><br>

<label for="fav5370">CTC Analytics / Leap Technologies Combi PAL Autosampler for Liquid and Headspace Injections</label><input style="width: 98%" name="field_4[]" id="fav5370" type="text" value="Add question..."><br>

</li>

Anything glaringly wrong? Thanks in advance.