How unrequire comment text in wordpress post

Question

I made a few comment meta field and they work well.

Now I need to set comment text as no require.

I found this solution but don't work for me.

add_action( 'pre_comment_on_post', 'allow_empty_comment_text' );

function allow_empty_comment_text( $text = '' )
{
    if ( ! isset ( $_POST['comment'] ) or '' === trim( $_POST['comment'] ) )
    {
        $img = '/* Process uploaded image here, create an <img> tag. */'    
        $_POST['comment'] = '<img>'; // use a real img tag here
    }
}

any solution please.

Answer 1

I solve it:

step 1 - insert a random number in text body, because WordPress prevent users that duplicate comments.

step 2- set display:none to textarea of comment field

Finally copy this code in functions.php:

add_filter( 'comment_form_field_comment', 'set_default_comment_text', 10, 1 );

function set_default_comment_text() {

    $post_id = get_the_title();

    global $current_user;

    get_currentuserinfo();

    $comment_rand = rand(10,100000);

    $comment_field = '<textarea style="display:none" id="comment" name="comment" cols="45" rows="8" maxlength="65525" readonly="readonly">'.$comment_rand.'</textarea>';

    return $comment_field;
}

Answer 2

I think you can use $_POST['comment'] = 'NO_COMMENT' then when display the comment you strip that string by "comment_text" filter.