Custom Field thumbnails broken…

$url is set to an empty string at the top of the foreach loop, but is never given a value inside the if ( $thsource == ‘custom-field’ ) { … } section of code…

    foreach ( $posts as $post ) {
        $image = '';
        $url   = '';
        $alt   = '';
        if ( $thsource == 'custom-field' ) {
          if ( is_array( $url ) ) {
              $debug .= 'No custom field specifield, using default thumbnail image;';
              $url = $this->default_image;
          } else {
              $debug .= 'Using custom field;';
              $theme_resize_url = get_option( 'relpoststh_theme_resize_url', '' );
              
              if ( strpos( $url, '/wp-content' ) !== false ) {
                $url = substr( $url, strpos( $url, '/wp-content' ) );
              }
              
              if ( !empty( $theme_resize_url ) ) {
                $url = $theme_resize_url . '?src=' . $url . '&w=' . $width . '&h=' . $height . '&zc=1&q=90';
              }
          }
        } else {