### Question:
LocalDateDoubleTimeSeriesBuilder { public LocalDateDoubleTimeSeries build() { if (entries.isEmpty()) { return LocalDateDoubleTimeSeries.empty(); } return density() > DENSITY_THRESHOLD ? createDenseSeries() : createSparseSeries(); } LocalDateDoubleTimeSeriesBuilder();   LocalDateDoubleTimeSeriesBuilder(LocalDate[] dates, double[] values);   LocalDateDoubleTimeSeriesBuilder(Stream<LocalDateDoublePoint> points); OptionalDouble get(LocalDate date); LocalDateDoubleTimeSeriesBuilder put(LocalDate date, double value); LocalDateDoubleTimeSeriesBuilder put(LocalDateDoublePoint point); LocalDateDoubleTimeSeriesBuilder merge(LocalDate date, double value, DoubleBinaryOperator operator); LocalDateDoubleTimeSeriesBuilder merge(LocalDateDoublePoint point, DoubleBinaryOperator operator); LocalDateDoubleTimeSeriesBuilder putAll(Collection<LocalDate> dates, Collection<Double> values); LocalDateDoubleTimeSeriesBuilder putAll(Collection<LocalDate> dates, double[] values); LocalDateDoubleTimeSeriesBuilder putAll(Stream<LocalDateDoublePoint> points); LocalDateDoubleTimeSeriesBuilder putAll(List<LocalDateDoublePoint> points); LocalDateDoubleTimeSeriesBuilder putAll(LocalDateDoubleTimeSeriesBuilder other); LocalDateDoubleTimeSeriesBuilder putAll(Map<LocalDate, Double> map); LocalDateDoubleTimeSeries build();  }### Answer:
@Test public void test_buildEmptySeries() { assertThat(LocalDateDoubleTimeSeries.builder().build()).isEqualTo(LocalDateDoubleTimeSeries.empty()); }