docs: protected UnmappedReads<Read> getUnmappedMatesOfMappedReads(String readsetId) 
        throws GeneralSecurityException, IOException {
      LOG.info("Collecting unmapped mates of mapped reads for injection");
      final Iterable<Read> unmappedReadsIterable = getUnmappedReadsIterator(readsetId); 
      final UnmappedReads<Read> unmappedReads = createUnmappedReads();
      for (Read read : unmappedReadsIterable) {
        unmappedReads.maybeAddRead(read);
      }
      LOG.info("Finished collecting unmapped mates of mapped reads: " + 
          unmappedReads.getReadCount() + " found.");
      return unmappedReads;
    }