Getting post content within wp_nav_walker

Question

I have a custom walker set up designed to add content into the nav menu. The problem being that it is not pulling the content. The post object returned by the get_post/get_page has an empty post_content attribute. What is causing this?

Walker:

class mobile_walker_nav_menu extends Walker_Nav_Menu {



function start_lvl( &$output, $depth ) {
// depth dependent classes
$indent = ( $depth > 0  ? str_repeat( "\t", $depth ) : '' ); // code indent
$display_depth = ( $depth + 1); // because it counts the first submenu as 0
$classes = array(
    'sub-menu',
    ( $display_depth % 2  ? 'menu-odd' : 'menu-even' ),
    ( $display_depth >=2 ? 'sub-sub-menu' : '' ),
    'menu-depth-' . $display_depth
    );
$class_names = implode( ' ', $classes );

// build html
$output .= "\n" . $indent . '<ul class="' . $class_names . '">' . "\n";
}


function start_el( &$output, $item, $depth, $args ) {
global $wp_query;
$indent = ( $depth > 0 ? str_repeat( "\t", $depth ) : '' ); // code indent

// depth dependent classes
$depth_classes = array(
    ( $depth == 0 ? 'main-menu-item' : 'sub-menu-item' ),
    ( $depth >=2 ? 'sub-sub-menu-item' : '' ),
    ( $depth % 2 ? 'menu-item-odd' : 'menu-item-even' ),
    'menu-item-depth-' . $depth
);


$depth_class_names = esc_attr( implode( ' ', $depth_classes ) );

// passed classes
$classes = empty( $item->classes ) ? array() : (array) $item->classes;
$class_names = esc_attr( implode( ' ', apply_filters( 'nav_menu_css_class', array_filter( $classes ), $item ) ) );
// build html
$output .= $indent . '<li id="nav-menu-item-'. $item->ID . '" class="' . $depth_class_names . ' ' . $class_names . ' ' . $theBack . '">';

// link attributes
$attributes  = ! empty( $item->attr_title ) ? ' title="'  . esc_attr( $item->attr_title ) .'"' : '';
$attributes .= ! empty( $item->target )     ? ' target="' . esc_attr( $item->target     ) .'"' : '';
$attributes .= ! empty( $item->xfn )        ? ' rel="'    . esc_attr( $item->xfn        ) .'"' : '';
$attributes .= ! empty( $item->url )        ? ' href="'   . esc_attr( $item->url        ) .'"' : '';
$attributes .= ' class="menu-link ' . ( $depth > 0 ? 'sub-menu-link' : 'main-menu-link' ) . ' ' . $class_names . '"';

$item_output = sprintf( '%1$s<a%2$s>%3$s%4$s%5$s</a>%6$s',
    $args->before,
    $attributes,
    $args->link_before,
    apply_filters( 'the_title', $item->title, $item->ID ),
    $args->link_after,
    $args->after
);

// build html
$output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args );

$output .= '<div class="slidedown">';
var_dump(get_page($item->ID));
if(is_page($item->ID)){
        $the_page = get_page($item->ID);
        var_dump($the_page);
        $output .= apply_filters('the_content', $the_page->post_content);
} elseif (is_single($item->ID)){
        $the_post = get_post($item->ID); 
        $output .= apply_filters('the_content', $the_post->post_content);
}
}

function end_el( &$output, $item, $depth = 0, $args = array() ) {
    $output .= "</div></li>\n";
}
}