@Override
    public E computeIfAbsent(String key, Function<? super String, ? extends E> mappingFunction) {
        try {
            return cacheStore.invoke(key, new AtomicComputeProcessor<>(), mappingFunction);
        } catch (EntryProcessorException e) {
            throw new RuntimeException(e.getCause());
        }
    }
@Test
    public void computeIfAbsent_cacheMiss_mappingFunctionReturnsNull_returnOldValue() {
        Function<String, Integer> mappingFunction = k -> null;
        doReturn(null).when(mutableEntryMock).getValue();
        entryProcessorMock = new CacheRegistryStore.AtomicComputeProcessor<>();
        entryProcessorArgMock = mappingFunction;

        Integer cacheResult = classUnderTest.computeIfAbsent(CACHE_KEY, mappingFunction);

        verify(mutableEntryMock, never()).setValue(any());
        assertNull(cacheResult);
    }