Source

File: wp-includes/rest-api/endpoints/class-wp-rest-revisions-controller.php

protected function get_revision( $id ) {
		$error = new WP_Error(
			'rest_post_invalid_id',
			__( 'Invalid revision ID.' ),
			array( 'status' => 404 )
		);

		if ( (int) $id <= 0 ) {
			return $error;
		}

		$revision = get_post( (int) $id );
		if ( empty( $revision ) || empty( $revision->ID ) || 'revision' !== $revision->post_type ) {
			return $error;
		}

		return $revision;
	}