public Iterator<Entry<String, Optional<MetaProperties>>> nonFailedDirectoryProps() {
        return new Iterator<Entry<String, Optional<MetaProperties>>>() {
            private final Iterator<String> emptyLogDirsIterator = emptyLogDirs.iterator();
            private final Iterator<Entry<String, MetaProperties>> logDirsIterator =
                    logDirProps.entrySet().iterator();

            @Override
            public boolean hasNext() {
                return emptyLogDirsIterator.hasNext() || logDirsIterator.hasNext();
            }

            @Override
            public Entry<String, Optional<MetaProperties>> next() {
                if (emptyLogDirsIterator.hasNext()) {
                    return new SimpleImmutableEntry<>(emptyLogDirsIterator.next(), Optional.empty());
                }
                Entry<String, MetaProperties> entry = logDirsIterator.next();
                return new SimpleImmutableEntry<>(entry.getKey(), Optional.of(entry.getValue()));
            }
        };
    }
@Test
    public void testNonFailedDirectoryPropsForEmpty() {
        assertFalse(EMPTY.nonFailedDirectoryProps().hasNext());
    }