code: public Datapoint addDoubleValue(long time, double value) {
          initialValues();
          checkType(TsdbConstants.TYPE_DOUBLE);
  
          values.add(Lists.<JsonNode> newArrayList(new LongNode(time), new DoubleNode(value)));
          return this;
      }
docs: Add datapoint of double type value.
  
  @param time datapoint's timestamp
  @param value datapoint's value
  @return Datapoint