src/properties/class-papi-property-user.php
public function update_value( $value, $slug, $post_id ) {
		if ( $value instanceof WP_User ) {
			$value = $value->ID;
		}

		return (int) $value;
	}
public function update_value( $value, $slug, $post_id ) {
		if ( $value instanceof WP_User ) {
			$value = $value->ID;
		}

		return (int) $value;
	}
Update value before it's saved to the database.

@param mixed  $value
@param string $slug
@param int    $post_id

@return int