Duplicate posts when posting nulls in records in phpMyAdmin

I have a phpMyAdmin database with a table whose contents, when inputted from the database, automatically publish the related information.

Some of the details within the record may be NULL, and while testing I encountered the issue that if any of the content within any record is NULL, all the records are duplicated when reloading from wp-admin. The number of records within the database remains unchanged.

I am quite sure there is a way to deal with NULLS in this context but I am very inexperienced with WordPress and PHP in general and could not find a relevant topic on it.

Below is the relevant code and screenshots to better explain the context:

Publication-CPT.php (plugin)

if(!function_exists('add_action'))
{
    echo 'ERROR: ABSPATH UNDEFINED. Access to this file is not allowed.';
    exit;
}

function create_abstract_cpt() {

    $labels = array(
        'name' = _x( 'Abstracts', 'Post Type General Name', 'textdomain' ),
        'singular_name' = _x( 'Abstract', 'Post Type Singular Name', 'textdomain' ),
        'menu_name' = _x( 'Abstracts', 'Admin Menu text', 'textdomain' ),
        'name_admin_bar' = _x( 'Abstract', 'Add New on Toolbar', 'textdomain' ),
        'archives' = __( 'Abstract Archives', 'textdomain' ),
        'attributes' = __( 'Abstract Attributes', 'textdomain' ),
        'parent_item_colon' = __( 'Parent Abstract:', 'textdomain' ),
        'all_items' = __( 'All Abstracts', 'textdomain' ),
        'add_new_item' = __( 'Add New Abstract', 'textdomain' ),
        'add_new' = __( 'Add New', 'textdomain' ),
        'new_item' = __( 'New Abstract', 'textdomain' ),
        'edit_item' = __( 'Edit Abstract', 'textdomain' ),
        'update_item' = __( 'Update Abstract', 'textdomain' ),
        'view_item' = __( 'View Abstract', 'textdomain' ),
        'view_items' = __( 'View Abstracts', 'textdomain' ),
        'search_items' = __( 'Search Abstract', 'textdomain' ),
        'not_found' = __( 'Not found', 'textdomain' ),
        'not_found_in_trash' = __( 'Not found in Trash', 'textdomain' ),
        'featured_image' = __( 'Featured Image', 'textdomain' ),
        'set_featured_image' = __( 'Set featured image', 'textdomain' ),
        'remove_featured_image' = __( 'Remove featured image', 'textdomain' ),
        'use_featured_image' = __( 'Use as featured image', 'textdomain' ),
        'insert_into_item' = __( 'Insert into Abstract', 'textdomain' ),
        'uploaded_to_this_item' = __( 'Uploaded to this Abstract', 'textdomain' ),
        'items_list' = __( 'Abstracts list', 'textdomain' ),
        'items_list_navigation' = __( 'Abstracts list navigation', 'textdomain' ),
        'filter_items_list' = __( 'Filter Abstracts list', 'textdomain' ),
    );
    $args = array(
        'label' = __( 'Abstract', 'textdomain' ),
        'description' = __( 'List of all the abstracts', 'textdomain' ),
        'labels' = $labels,
        'menu_icon' = 'dashicons-text',
        'supports' = array('title', 'editor', 'excerpt', 'thumbnail', 'author', 'post-formats', 'custom-fields'),
        'public' = true,
        'show_ui' = true,
        'show_in_menu' = true,
        'menu_position' = 5,
        'show_in_admin_bar' = true,
        'show_in_nav_menus' = true,
        'can_export' = true,
        'has_archive' = true,
        'hierarchical' = false,
        'exclude_from_search' = false,
        'show_in_rest' = true,
        'publicly_queryable' = true,
        'capability_type' = 'post',
        'taxonomies' = array( 'category', 'post_tag' ),
    );
    flush_rewrite_rules();
    register_post_type( 'abstract', $args );

}
add_action( 'init', 'create_abstract_cpt', 0 );

add_action( 'wp', 'insert_into_cpt');

function verify_existing_abstract_in_cpt() 
{

    $id_arrays_in_cpt = [];
    // Query all autos
    $args = array(
        'post_type'      = 'abstract',
        'posts_per_page' = -1,
    );

    $loop = new WP_Query($args);
    while ( $loop-have_posts() ) {
        $loop-the_post();
        $id_arrays_in_cpt[] = get_post_meta( get_the_ID(), 'abstract_id', true);
    }
    return $id_arrays_in_cpt;
}

function query_abstract_post_table( $available_in_cpt ) 
{
    // Query Database
    global $wpdb;
    $table_name = $wpdb-prefix . 'abstract_posts';
    if ( NULL === $available_in_cpt || empty($available_in_cpt) || 0 === $available_in_cpt) {
        $sql = SELECT * FROM $table_name;
    } else {
        $ids = implode( ,, $available_in_cpt);
        $sql = SELECT * FROM $table_name WHERE abstract_id NOT IN ('$ids');
    }

    $results = $wpdb-get_results( $sql );
    return $results;
}

function insert_into_cpt()
{
    //If the queried results from do not match the existing abstracts
    $available_in_cpt = verify_existing_abstract_in_cpt();
    $database_results = query_abstract_post_table( $available_in_cpt );

    //Insert into CPT
    foreach($database_results as $result) 
    {
        // Create post object
        $abstract_details = array(
            'post_title' = $result-title,
            'meta_input' = array(
                'abstract_id' = $result-abstract_id,
                'title' = $result-title,
                'author' = $result-author,
                'supervisor' = $result-supervisor,
                'cosupervisor' = $result-cosupervisor,
                'course' = $result-course,
                'categ' = $result-categ,
                'writeup' = $result-writeup,
                'firstabstractimage' = $result-firstabstractimage,
                'firstabstractimagecaption' = $result-firstabstractimagecaption,
                'secondabstractimage' = $result-secondabstractimage,
                'secondabstractimagecaption' = $result-secondabstractimagecaption,
                'ref' = $result-ref,
            ),
            'post_type'   = 'abstract',
            'post_status' = 'publish',
        );
        //Insert into wp_insert_post
        wp_insert_post( $abstract_details );
    }
}

wp_abstract_posts (Table) - Inclusion of NULL in any record causes this issue

Abstracts CPT posts (duplication of all posts when refreshing wp-admin in any fashion)

Any help would be greatly appreciated.