/**
     * @param iterable<array<string, mixed>> $saveDocuments
     * @param iterable<string> $deleteDocumentIdentifiers
     * @param array{return_slow_promise_result?: true} $options
     *
     * @return ($options is non-empty-array ? TaskInterface<array<string, mixed>> : null)
     */
    public function bulk(
        Index $index,
        iterable $saveDocuments,
        iterable $deleteDocumentIdentifiers,
        int $bulkSize = 100,
        array $options = [],
    ): TaskInterface|null;