ParallelStream and multiple calls in the mapper

Question

I am trying to build a list of responses from a list of entities (DB).

To construct my list of responses, I am using parallelStream and in the mapper, I am trying to call another microservice but the problem is that only one result is injected into my response instead of each item response in the list.

Use case

companyPartnerships.parallelStream()
            .map(partnershipItemMapper::toPartnershipItemResponse)
            .collect(Collectors.toList());

Mapper

@Mapping(target = "balance", source = ".", qualifiedByName = "injectBalanceToPartnershipItemResponse")
public abstract PartnershipItemResponse toPartnershipItemResponse(Partnership partnership);

@Named("injectBalanceToPartnershipItemResponse")
protected Long injectBalanceToPartnershipItemResponse(Partnership partnership) {
    return partnershipMetricsProxy.getPartnershipMetricsFor(partnership.getId())
        .map(PartnershipMetrics::getBalance)
        .orElse(null);
}

Example of response

    {
        "id": 473,
        "balance": null
    },
    {
        "id": 617,
        "balance": 26122
    },
    {
        "id": 517,
        "balance": null
    }