WP_REST_Settings_Controller::update_item( WP_REST_Request $request )

	public function update_item( $request ) {
		$options = $this->get_registered_options();

		$params  = $request->get_params();

		foreach ( $options as $name => $args ) {
			if ( ! array_key_exists( $name, $params ) ) {
				continue;
			}

			/**
			 * Filters whether to preempt a setting value update.
			 *
			 * Allows hijacking the setting update logic and overriding the built-in behavior by
			 * returning true.
			 *
			 * @since WP-4.7.0
			 *
			 * @param bool   $result Whether to override the default behavior for updating the
			 *                       value of a setting.
			 * @param string $name   Setting name (as shown in REST API responses).
			 * @param mixed  $value  Updated setting value.
			 * @param array  $args   Arguments passed to register_setting() for this setting.
			 */
			$updated = apply_filters( 'rest_pre_update_setting', false, $name, $request[ $name ], $args );

			if ( $updated ) {
				continue;
			}

			/*
			 * A null value for an option would have the same effect as
			 * deleting the option from the database, and relying on the
			 * default value.
			 */
			if ( is_null( $request[ $name ] ) ) {
				/*
				 * A null value is returned in the response for any option
				 * that has a non-scalar value.
				 *
				 * To protect clients from accidentally including the null
				 * values from a response object in a request, we do not allow
				 * options with values that don't pass validation to be updated to null.
				 * Without this added protection a client could mistakenly
				 * delete all options that have invalid values from the
				 * database.
				 */
				if ( is_wp_error( rest_validate_value_from_schema( get_option( $args['option_name'], false ), $args['schema'] ) ) ) {
					return new WP_Error(
						'rest_invalid_stored_value', sprintf( __( 'The %s property has an invalid stored value, and cannot be updated to null.' ), $name ), array( 'status' => 500 )
					);
				}

				delete_option( $args['option_name'] );
			} else {
				update_option( $args['option_name'], $request[ $name ] );
			}
		}

		return $this->get_item( $request );
	}