code: public static Hasher putLabels(Hasher h, Map<String, String> labels) {
      for (Map.Entry<String, String> labelsEntry : labels.entrySet()) {
        h.putChar('\0');
        h.putString(labelsEntry.getKey(), StandardCharsets.UTF_8);
        h.putChar('\0');
        h.putString(labelsEntry.getValue(), StandardCharsets.UTF_8);
      }
      return h;
    }
docs: Updates {@code h} with the contents of {@code labels}.
  
  {@code labels} can be any Map&lt;String, String&gt;, but intended to be used for the labels of
  one of the model protobufs.
  
  @param h a {@link Hasher}
  @param labels some labels
  @return the {@code Hasher}, to allow fluent-style usage