function dozent_query_vars( $query_var = null ) {

		$registered_vars = dozent_register_query_vars();
		$in_request      = [];

		if ( dozent_count( $registered_vars ) ) {
			foreach ( $registered_vars as $var ) {
				$var_in_request = get_query_var( $var );
				if ( $var_in_request ) {
					$in_request[ $var ] = $var_in_request;
				}
			}
		}

		if ( $query_var ) {
			$query_var_in_request = get_query_var( $query_var, $in_request );

			return apply_filters( 'dozent_query_var', $query_var_in_request, $query_var );
		}

		return apply_filters( 'dozent_query_vars', $in_request );
	}