wp_nav_menu returns false even though a menu is assigned to it

Question

I'm developing a new theme and am encountering a weird behaviour.

I have registered a footer menu:

register_nav_menus([
                'primary_navigation' => "Main nav",
                'footer_navigation' => "Footer nav"
                ]);

In the template, primary_navigation menu shows correctly the custom menu created in the Administration zone.

But footer_navigation does not. In fact, it returns false:

if (has_nav_menu('footer_navigation')) {
?>
    <ul class="c-footnav__list flex-container" role="navigation">

<?php   

    if(!wp_nav_menu( array( 'theme_location' => 'footer_navigation', 'depth'=>10, 'echo'=>true ))){

    echo "could not print menu";    
        }; ?>

    </ul>

<?php
 }

It prints the <UL> element and the "could not print menu" message.

The documentation regarding wp_nav_menu() says:

(object|false|void) Menu output if $echo is false, false if there are no items or no menu was found.

So I must assume that it does not find the menu. But why then the call to has_nav_menu('footer_navigation') returns true ? What am I missing?

Answer 1

It turns out the fault was all mine.

I was attaching a callback function to the wp_nav_menu_items hook that returned empty if it wasn't the main menu... This was it:

// Add logo in main menu

 add_filter( 'wp_nav_menu_items', 'add_logo_in_main_menu', 10, 2 );



function add_logo_in_main_menu( $items, $menu ){
    /*
        Append logo to main menu
    */
        if(is_admin() ||  'primary_navigation' !== $menu->theme_location){
            return;  //<!--- in this case, returns nothing
        }
        return '<li class="c-logo--medium"><img src="'.get_stylesheet_directory_uri().'/assets/images/logo-pm.jpg" alt=""></li>'. $items;

    }

The fix was easy:

function add_logo_in_main_menu( $items, $menu ){
        /*
        Append logo to main menu
        */
        if(is_admin() ||  'primary_navigation' !== $menu->theme_location){
            return $items;
        }
        return '<li class="c-logo--medium"><img src="'.get_stylesheet_directory_uri().'/assets/images/logo-pm.jpg" alt=""></li>'. $items;

    }

Sorry for the noise.