functions.php

<?php

// Link directly to Media files instead of Attachment pages in search results
function my_search_media_direct_link( $permalink, $post = null ) {
	if ( ( is_search() || doing_action( 'wp_ajax_searchwp_live_search' )
	      || doing_action( 'wp_ajax_nopriv_searchwp_live_search' ) )
	    && 'attachment' === get_post_type( $post ) ) {
		$permalink = wp_get_attachment_url( $post );
	}

	return esc_url( $permalink );
}

add_filter( 'the_permalink',   'my_search_media_direct_link', 99, 2 );
add_filter( 'attachment_link', 'my_search_media_direct_link', 99, 2 );

I found a solution. I just changed

function my_search_media_direct_link( $permalink, $post )
to
function my_search_media_direct_link( $permalink, $post = null )

so the second argument would be null if the argument was missing.

Hopefully this helps someone else out! Thanks for a great plugin!