cmb2_initial_value.php

<?php

/**
 * CMB2 delete value instead of saving empty value. So fields with default value cannot hold empty value.
 * This example works around this issue by adding new field parameter `initial value'.
 *
 * Example:
 *      $cmb->add_field( array(
 *          'name'          => 'Title for publish',
 *          'initial_value' => '%d product(s) published',
 *          'id'            => 'title_publish',
 *          'type'          => 'text',
 *      ) );
 *
 * @link https://gist.github.com/chrono-meter/225ee7a59af96775dbcfd0de0f01fbca
 */
class Cmb2_initial_value {
	function __construct() {
		add_action( 'cmb2_before_field_row', array( $this, 'cmb2_before_field_row' ) );
		add_action( 'cmb2_after_field_row', array( $this, 'cmb2_after_field_row' ) );
	}

	/**
	 * @param CMB2_Field $field The current field object.
	 */
	function cmb2_before_field_row( $field ) {
		$field_type = $field->type();
		add_filter( "cmb2_types_esc_{$field_type}", array( $this, 'cmb2_types_esc' ), 10, 4 );
	}

	/**
	 * @param CMB2_Field $field The current field object.
	 */
	function cmb2_after_field_row( $field ) {
		$field_type = $field->type();
		remove_filter( "cmb2_types_esc_{$field_type}", array( $this, 'cmb2_types_esc' ), 10 );
	}

	/**
	 * @param mixed $override_value Escaping override value to return. Default: null. false to skip it.
	 * @param mixed $meta_value The value to be output.
	 * @param array $field_args The current field's arguments.
	 * @param object $field This `CMB2_Field` object.
	 *
	 * @return mixed
	 *
	 * @see CMB2_Field::escaped_value()
	 */
	function cmb2_types_esc( $override_value, $meta_value, $field_args, $field ) {
		if ( isset( $field_args['initial_value'] ) ) {
			return get_post_status( $field->object_id ) == 'auto-draft' ? $field_args['initial_value'] : $meta_value;
		}

		return $override_value;
	}

}

new Cmb2_initial_value();