Invalid argument supplied for foreach() in search.php

Because get_the_terms will not always return an array; it will be false if the post has no terms, or a WP_Error if the taxonomy does not exist – always sanity check the result before looping:

$terms_slugs = array();
$terms = get_the_terms( $post->id, 'type', /* Note: get_the_terms does not take a 3rd argument ==> */ array( 'parent' => 0 ) );

if ( is_array( $terms ) ) {
    foreach ( $terms as $term ) {
        $terms_slugs[] = $term->slug;
    }
}

Better yet, in this case you can use the awesome helper wp_list_pluck():

if ( is_array( $terms = get_the_terms( $post->ID, 'type' ) ) )
    $terms_slugs = wp_list_pluck( $terms, 'slug' );
else
    $terms_slugs = array();