protected function toArrayCustom( $arr ) {

		// Build an array of keys that are registered or can be excluded as a custom field.
		$props = array_keys( $this->get_properties() );
		foreach ( $props as &$prop ) {
			$prop = $this->meta_prefix . $prop;
		}
		$props[] = '_edit_lock';
		$props[] = '_edit_last';

		// Get all meta data.
		$custom = array();
		foreach ( get_post_meta( $this->get( 'id' ) ) as $key => $vals ) {

			// Skip registered fields or fields 3rd parties want to skip.
			/**
			 * Filters whether the custom field should be excluded in the array representation of the post model
			 *
			 * The dynamic portion of this hook, `$this->model_post_type`, refers to the model's post type. For example "course",
			 * "lesson", "membership", etc...
			 *
			 * @since 3.30.2
			 *
			 * @param boolean         $exclude   Whether the custom field should be excluded. Default is `false`.
			 * @param string          $key       The custom field name.
			 * @param LLMS_Post_Model $llms_post The LLMS_Post_Model instance.
			 */
			if ( in_array( $key, $props, true ) || apply_filters( "llms_{$this->model_post_type}_skip_custom_field", false, $key, $this ) ) {
				continue;
			}

			// Add it.
			$custom[ $key ] = array_map( 'maybe_unserialize', $vals );

		}

		// Add the compiled custom array.
		$arr['custom'] = $custom;

		return $arr;
	}