How do you return a menu with the menu name?

How do you return a menu with the menu name?

in functions.php, I've defined the following:
register_nav_menu( 'home_blocks', __( 'Home Page Posts', 'my_Theme' ) );
In /wp-admin/nav-menus.php, I've added a menu called Home Page Posts and assigned 3 posts to it and set it to be the item associated with Home Page Posts as the menu location.
In index.php, I've added the following:
if ( has_nav_menu( 'primary' ) ) {
    echo 'has primary<br />';
} else {
    echo 'no primary<br />';
}
if ( has_nav_menu( 'home_blocks' ) ) {
    echo 'has home blocks<br />';
} else {
    echo 'no home_blocks<br />';
}
Both of the successful conditions are echoed.
When I try to return the menu contents so I can run some inline custom output based on post_id, I attempted the following code and got NULL or string(0) "", depending on what values I put for the location and menu name. What way are these values associated and how would I get the menu back?
$defaults = array(
    'theme_location'  => 'home_blocks',
    'menu'            => '',
    'container'       => '',
    'container_class' => '',
    'container_id'    => '',
    'menu_class'      => '',
    'menu_id'         => '',
    'echo'            => 1,
    'fallback_cb'     => '',
    'before'          => '',
    'after'           => '',
    'link_before'     => '',
    'link_after'      => '',
    'items_wrap'      => '',
    'depth'           => 0,
    'walker'          => ''
);

$menu = wp_nav_menu( $defaults );

var_dump( $menu );