WordPress CMB2 Terms as Options

cmb2-box.php

 <?php
 $cmb2->add_field(
    array(
        'id'            => '_[id]',
		'name'          => '',
        'type'          => '',
        'options_cb'    => __NAMESPACE__ . '\\get_term_options',
        'get_term_args' => array(
            'taxonomy'   => '',
            'hide_empty' => false,
        ),
    )
 );

cmb2-term-options.php

<?php
/**
 * Gets a number of terms and displays them as options.
 *
 * @param  CMB2_Field $field The CMB2 field.
 * @return array An array of options that matches the CMB2 options array.
 */
function get_term_options( $field ) {
	$args = $field->args( 'get_term_args' );
	if ( empty( $args ) ) {
		return;
	}

	$terms       = get_terms( $args );
	$term_return = array();

	if ( ! empty( $terms ) ) {
		foreach ( $terms as $term ) {
			$term_return[ $term->term_id ] = $term->name;
		}
	}

	return $term_return;
}