### Question:
ExpressionGridCacheImpl extends AbstractCanvasControl<AbstractCanvas> implements ExpressionGridCache { @Override public Optional<BaseExpressionGrid<? extends Expression, ? extends GridData, ? extends BaseUIModelMapper>> getExpressionGrid(final String nodeUUID) { return cache.getOrDefault(nodeUUID, Optional.empty()); } ExpressionGridCacheImpl(); @Override Optional<BaseExpressionGrid<? extends Expression, ? extends GridData, ? extends BaseUIModelMapper>> getExpressionGrid(final String nodeUUID); @Override void putExpressionGrid(final String nodeUUID,
                                  final Optional<BaseExpressionGrid<? extends Expression, ? extends GridData, ? extends BaseUIModelMapper>> gridWidget); @Override void removeExpressionGrid(final String nodeUUID);  }### Answer:
@Test public void testGetExpressionWhenNotPresent() { assertThat(cache.getExpressionGrid("")).isNotPresent(); }