Set<VCFHeaderLine> headerLines = new HashSet<VCFHeaderLine>();
if ( SET_KEY != null )
headerLines.add(new VCFInfoHeaderLine(SET_KEY, 1, VCFHeaderLineType.String, "Source VCF for the merged record"));
if ( STATUS_KEY != null )
headerLines.add(new VCFInfoHeaderLine(STATUS_KEY, 1, VCFHeaderLineType.String, "Extent to which records match"));
final VCFHeader vcfHeader = new VCFHeader(headerLines, Collections.<String>emptySet());
baseWriter.writeHeader(vcfHeader);
writer = VariantContextWriterFactory.sortOnTheFly(baseWriter, ACTIVE_WINDOW);
}