Add value to field using hook_webform_submission_presave()

I am at my wits end trying to use the hook_webform_submission_presave function on a webform that I have created for a Drupal 7 site. Ideally I would like to capture a list of nodes that a user has flagged and transfer that data into a field before the user submits their form. But the function is just not adding the data.

First I get the flags:

$flags = flag_get_user_flags($node->type);

Then I want to transfer that variable into a field with a component ID of 30.

// Update some component's value before it is saved.
  $component_id = 30;
  $submission->data[$component_id]['value'][0] = $flags;

Here is the full function:

function MYMODULE_webform_submission_presave($node, &$submission) {
    $nodes_list = array();
    $title = '';
  // Get the flags.
  $flags = flag_get_user_flags($node->type);

  // Update some component's value before it is saved.
  $component_id = 30;
  $submission->data[$component_id]['value'][0] = $flags;
}

What am I doing wrong? I'd love some help!