Odin_Metabox on about page

about-meta-box.php

<?php

function about_metabox_page () {
    $hasGetMethod = (isset($_GET['post']) && !empty($_GET['post']));
    $hasPostMethod = (isset($_POST['post_ID']) && !empty($_POST['post_ID']));
    $about_pages_arr = array(
        'sobre',
        'sobre-nos',
        'sobre-a-grgit',
        'quem-somos',
        'about',
        'about-us'
    );

    if ($hasGetMethod || $hasPostMethod) {
        $post_ID = $hasGetMethod ? $_GET['post'] : $_POST['post_ID'];
        $post = get_post( $post_ID );
        $slug = $post->post_name;

        if( in_array( $slug, $about_pages_arr ) ) {
            /* Metaboxes for about page */
            $about_metabox = new Odin_Metabox(
                'about',
                'Missão/Visão/Valores',
                'page',
                'normal',
                'high'
            );
            $about_metabox->set_fields(
                array(
                    array(
                        'id' => 'about_missao',
                        'label' => __( 'Missão', 'grgit' ),
                        'type' => 'textarea'
                    ),
                    array(
                        'id' => 'about_visao',
                        'label' => __( 'Visão', 'grgit' ),
                        'type' => 'textarea'
                    ),
                    array(
                        'id' => 'about_valores',
                        'label' => __( 'Valores', 'grgit' ),
                        'type' => 'textarea'
                    )
                )
            );
        }
    }
}

add_action( 'init', 'about_metabox_page' );