Ajax WP_Query reutrns no results on author.php

Well i figured it out somehow. There were two causes to that issue:

1. tax_query array values cannot be empty. it either the array keys are populated, or there shouldn’t be an array at all.

2. I don’t know why, but giving author a number didn’t work. I’ve changed it to 'author__in' => array($author) and it worked.

The fixed code altogether:

function bayadaim_ajax_fetch_posts(){
$template = $_POST['template'];
$offset = $_POST["offset"];
$ppp = $_POST["ppp"];
$tax = $_POST["tax"];
$term = $_POST["term"];

if( !empty($_POST["tax"]) || !empty($_POST["term"]) ){
$tax_query = array(array(
            'taxonomy' => $tax,
            'field'    => 'slug',
            'terms'    => $term,
        ),
    );
}else{
    $tax_query = null;
}
$meta = $_POST["meta"];
$author = $_POST["author"];
$orderby = $_POST["orderby"];
$order = $_POST["order"];
$post_type = (!empty($_POST["post_type"]) ? $_POST["post_type"] : "post");
header("Content-Type: text/html");

$args = array(
    'meta_key' => $meta,
    'orderby' => $orderby,
    'order' => $order, 
    'posts_per_page' => $ppp,
    'tax_query' => $tax_query,
    'author__in' => array($author),
    'offset' => $offset,
    'post_status' => 'publish',
    'post_type' => $post_type
);

$loop = new WP_Query($args);

if ($loop->have_posts()) :
    while ($loop->have_posts()) : $loop->the_post();
        if ( $template == 'row' ) {
            include( locate_template( 'content-post_in_row.php', false, true ) ); //by using include(locate_template()) combination i keep child-theme functionality while still passing variables to included file.
        }elseif( $template == 'list' ){
            include( locate_template( 'content-post_in_listing.php', false, true ) ); //by using include(locate_template()) combination i keep child-theme functionality while still passing variables to included file.                
        }
    endwhile;
else :
    if ( !empty($loop) ) print_r($loop); //for debugging
endif;

exit; 
}

add_action('wp_ajax_nopriv_bayadaim_ajax_fetch_posts', 'bayadaim_ajax_fetch_posts'); 
add_action('wp_ajax_bayadaim_ajax_fetch_posts', 'bayadaim_ajax_fetch_posts');

Any suggestions for how to make the code more elegant and efficient are welcomed.