Wordpress Front End Form to Publish/Draft Posts directly

I have a Wordpress Front End Form to Publish/Draft Posts directly from my theme: -

<?php
if( 'POST' == $_SERVER['REQUEST_METHOD'] && !empty( $_POST['action'] ) &&  $_POST['action'] == "new_post") {

    // Do some minor form validation to make sure there is content
    $title = $_POST["title"];
    if(!empty($_POST['middle'])) {
    $description = 'a sentence ' . $_POST['middle'] . ' with something in the MIDDLE. a sentence ' . $_POST['end'] . ' with something in the END.';
    }
    $tags = $_POST["tags"];
    $post_cat = $_POST['cat'];

    // ADD THE FORM INPUT TO $new_post ARRAY
    $new_post = array(
    'post_title'    =>  $title,
    'post_content'  =>  $description,
    'post_category' =>  $post_cat,  // Usable for custom taxonomies too
    'tags_input'    =>  $tags,
    'post_status'   =>  'draft',           // Choose: publish, preview, future, draft, etc.
    'post_type' =>  'post',  //'post',page' or use a custom post type if you want to
    );

    //SAVE THE POST
    $pid = wp_insert_post($new_post);

    //REDIRECT TO THE NEW POST ON SAVE
    $link = get_permalink( $pid );
    wp_redirect( '/post-submitted-draft' );

} // END THE IF STATEMENT THAT STARTED THE WHOLE FORM

//POST THE POST YO
do_action('wp_insert_post', 'wp_insert_post');

?>

PHP:

and I have a simple php form which has the following function: -

<?php
if(!empty($_POST['middle'])) {
   echo "a sentence".$_POST['middle']." with something in the MIDDLE.";
}

if(!empty($_POST['end'])) {
   echo "a sentence".$_POST['end']." with something in the END.";
}
?>

PHP:

I wanted to include it in the form and I did it using the method below: -

if(!empty($_POST['middle'])) {
$description = 'a sentence ' . $_POST['middle'] . ' with something in the MIDDLE. a sentence ' . $_POST['end'] . ' with something in the END.';

PHP:

but it will ignore the whole value of $description if the field of 'middle' is empty and I want it to ignore just the first sentence if the field of 'middle' is empty and display the second sentence which has the field of 'end' i.e.

'a sentence ' . $_POST['end'] . ' with something in the END.';

PHP:

How to make it work like this?