Function that replaces the image in the absence of the post meta

by

found the solution:

    $poster_path = get_post_meta($post->ID, "poster_path", $single = true);           
    if( $poster_path == "" ){ 
    echo '<img width="53" height="80" src="https://via.placeholder.com/370x556?text=No+Poster&000.jpg" />'; 
    } else {
    echo '<img width="53" height="80" src="https://image.tmdb.org/t/p/w370_and_h556_bestv2'.$poster_path.'" />';
    }