### Question:
UnitParameterSensitivity implements ImmutableBean, Serializable { public static UnitParameterSensitivity combine( MarketDataName<?> marketDataName, UnitParameterSensitivity... sensitivities) { ArgChecker.notEmpty(sensitivities, "sensitivities"); if (sensitivities.length < 2) { throw new IllegalArgumentException("At least two sensitivity instances must be specified"); } int size = Stream.of(sensitivities).mapToInt(s -> s.getParameterCount()).sum(); double[] combinedSensitivities = new double[size]; ImmutableList.Builder<ParameterMetadata> combinedMeta = ImmutableList.builder(); ImmutableList.Builder<ParameterSize> split = ImmutableList.builder(); int count = 0; for (int i = 0; i < sensitivities.length; i++) { UnitParameterSensitivity sens = sensitivities[i]; System.arraycopy(sens.getSensitivity().toArrayUnsafe(), 0, combinedSensitivities, count, sens.getParameterCount()); combinedMeta.addAll(sens.getParameterMetadata()); split.add(ParameterSize.of(sens.getMarketDataName(), sens.getParameterCount())); count += sens.getParameterCount(); } return new UnitParameterSensitivity( marketDataName, combinedMeta.build(), DoubleArray.ofUnsafe(combinedSensitivities), split.build()); } private  UnitParameterSensitivity(
      MarketDataName<?> marketDataName,
      List<? extends ParameterMetadata> parameterMetadata,
      DoubleArray sensitivity,
      List<ParameterSize> parameterSplit); static UnitParameterSensitivity of(
      MarketDataName<?> marketDataName,
      List<? extends ParameterMetadata> parameterMetadata,
      DoubleArray sensitivity); static UnitParameterSensitivity of(MarketDataName<?> marketDataName, DoubleArray sensitivity); static UnitParameterSensitivity of(
      MarketDataName<?> marketDataName,
      List<? extends ParameterMetadata> parameterMetadata,
      DoubleArray sensitivity,
      List<ParameterSize> parameterSplit); static UnitParameterSensitivity combine(
      MarketDataName<?> marketDataName,
      UnitParameterSensitivity... sensitivities); int getParameterCount(); ParameterMetadata getParameterMetadata(int parameterIndex); int compareKey(UnitParameterSensitivity other); CurrencyParameterSensitivity multipliedBy(Currency currency, double amount); UnitParameterSensitivity multipliedBy(double factor); UnitParameterSensitivity mapSensitivity(DoubleUnaryOperator operator); UnitParameterSensitivity withSensitivity(DoubleArray sensitivity); UnitParameterSensitivity plus(DoubleArray otherSensitivty); UnitParameterSensitivity plus(UnitParameterSensitivity otherSensitivty); ImmutableList<UnitParameterSensitivity> split(); double total(); static UnitParameterSensitivity.Meta meta(); @Override UnitParameterSensitivity.Meta metaBean(); MarketDataName<?> getMarketDataName(); ImmutableList<ParameterMetadata> getParameterMetadata(); DoubleArray getSensitivity(); Optional<List<ParameterSize>> getParameterSplit(); @Override boolean equals(Object obj); @Override int hashCode(); @Override String toString();  }### Answer:
@Test public void test_combine_arraySize0() { assertThatIllegalArgumentException() .isThrownBy(() -> UnitParameterSensitivity.combine(NAME_COMBINED)); }