code: public void setMissingMimeType(String missingMimeType) {
  		if (missingMimeType == null || missingMimeType.isEmpty())
  			this.missingMimeType = DEFAULT_MISSING_MIMETYPE;
  		else
  			this.missingMimeType = missingMimeType;
  	}
docs: Value of {@code mimetype} field indicating {@code Content-Type}
  is unavailable in the response.
  Default is {@code unk} (compatible with CDX-Writer).
  {@link IndexWorker} puts {@code application/http}, apparently.
  @param missingMimeType