self,
        embedding: list[float],
        k: int = 4,
        fetch_k: int = 20,
        lambda_mult: float = 0.5,
        param: Optional[dict] = None,
        expr: Optional[str] = None,
        timeout: Optional[int] = None,
        **kwargs: Any,
    ) -> List[Document]:
        """Perform a search and return results that are reordered by MMR.
        Args:
            embedding (str): The embedding vector being searched.
            k (int, optional): How many results to give. Defaults to 4.
            fetch_k (int, optional): Total results to select k from.
                Defaults to 20.
            lambda_mult: Number between 0 and 1 that determines the degree
                        of diversity among the results with 0 corresponding
                        to maximum diversity and 1 to minimum diversity.
                        Defaults to 0.5
            param (dict, optional): The search params for the specified index.
                Defaults to None.
            expr (str, optional): Filtering expression. Defaults to None.
            timeout (int, optional): How long to wait before timeout error.
                Defaults to None.
            kwargs: Collection.search() keyword arguments.
        Returns:
            List[Document]: Document results for search.
        """
        if self.col is None:
            logger.debug("No existing collection to search.")
            return []
        if param is None:
            param = self.search_params
        # Determine result metadata fields.
        output_fields = self.fields[:]
        output_fields.remove(self._vector_field)
        # Perform the search.
        res = self.col.search(
            data=[embedding],
            anns_field=self._vector_field,
            param=param,