Select All not working in a taxonomy search filter

I am trying to create a Search Filter within WordPress to filter through all the custom taxonomies within a Custom Post Type.

I have created a function that generates the dropdown so I can output each option value as a slug for my filter which is working already. My only issue is that the “Select All” option is not working.

The results come back with nothing found when Selecting All. The filter can be seen https://adoptapet.ie/pets/farms.

The code I have used to create the function is:

function adopt_custom_taxonomy_dropdown( $taxonomy, $orderby = 'date', $order = 'DESC', $limit = '-1', $name, $show_option_all = null, $show_option_none = null ) {
$args = array(
    'orderby' => $orderby,
    'order' => $order,
    'number' => $limit,

);
$terms = get_terms( $taxonomy, $args );
$name = ( $name ) ? $name : $taxonomy;
if ( $terms ) {
    printf( '<select name="%s" class="postform">', esc_attr( $name ) );
    if ( $show_option_all ) {
        printf( '<option value="0">%s</option>', esc_html( $show_option_all ) );
    }
    if ( $show_option_none ) {
        printf( '<option value="-1">%s</option>', esc_html( $show_option_none ) );
    }
    foreach ( $terms as $term ) {
        printf( '<option value="%s">%s</option>', esc_attr( $term->slug ), esc_html( $term->name ) );
    }
    print( '</select>' );
}
}

and this is where the search results are displayed:

<?php
        if (isset($_GET["farm-type"]) && empty($_GET["location-farms"])){

        $farm_type = $_GET["farm-type"];

        $myquery1['tax_query'] = array(
            array(
                'taxonomy' => 'farm-type',
                'terms' => array($farm_type),
                'field' => 'slug',

            ),
        );
        query_posts($myquery1);

        }
        ?>

        <?php
        if (isset($_GET["farm-type"]) && isset($_GET["location-farms"])){

        $farm_type = $_GET["farm-type"];
        $farm_location = $_GET["location-farms"];

        $myquery2['tax_query'] = array(
            array(
                'taxonomy' => 'farm-type',
                'terms' => array($farm_type),
                'field' => 'slug',
            ),
            array(
                'taxonomy' => 'location-farms',
                'terms' => array($farm_location),
                'field' => 'slug',
            ),
        );
        query_posts($myquery2);

        }
        ?>

Hopefully someone can help!