Optional.ofNullable doesn't seem to work if my inner objects are null?

SAGAR KALBURGI :

I have a nested class structure that I use to deserialize my data:

Class A has a single property that is an object of Class B (say b)
Class B has a single property that is an object of Class C (say c)
Class C has a single property that is an object of Class D (say d)
Class D has a single property that is a a string (say e)

I have data that looks like

Map<String, List<Map<String, Map<String, Map<String, Map<String, String>>>>>> input =
                ImmutableMap.of("Key",
                        ImmutableList.of(ImmutableMap.of("a",
                                ImmutableMap.of("b",
                                        ImmutableMap.of("c",
                                                ImmutableMap.of("d", "e"))))));

I want to parse this multilevel map and put the result into a map

Map<String, String> result = new HashMap<>();

At the end, I expect result map to contain this at the end: ["key", "e"]

I have this code that works if the map contain all the intermediate keys a, b, c and d

mapping.entrySet()
            .stream()
            .map(l -> l.getValue().stream()
                    .map(Optional::ofNullable)
                    .map(opta -> opta.map(A::getB))
                    .map(optb -> optb.map(B::getC))
                    .map(optc -> optc.map(C::getD))
                    .map(optd -> optd.map(D::getE))
                    .map(optv -> optv.orElse("default"))
                    .map(m -> result.put(l.getKey(), m))
                    .count())
            .count();

but for example say if the input is

Map<String, List<Map<String, Map<String, Map<String, Map<String, String>>>>>> input =
                    ImmutableMap.of("Key",
                        ImmutableList.of(ImmutableMap.of("a",
                                ImmutableMap.of("b",null))));

then my code fails:

java.lang.NullPointerException: null value in entry: b=null

Why is my Optional.isNullable not working?

NoDataFound :

You are using ImmutableMap, and ImmutableMap does not like null key or value: https://guava.dev/releases/23.0/api/docs/com/google/common/collect/ImmutableMap.html#of-K-V-

public static <K,V> ImmutableMap<K,V> of(K k1, V v1)

Returns an immutable map containing a single entry. This map behaves and performs comparably to Collections.singletonMap(K, V) but will not accept a null key or value. It is preferable mainly for consistency and maintainability of your code.

The message is produced by this method: https://github.com/google/guava/blob/82b3e9806dc3422e51ecb9400d8f50404b083dde/guava/src/com/google/common/collect/CollectPreconditions.java#L28

  static void checkEntryNotNull(Object key, Object value) {
    if (key == null) {
      throw new NullPointerException("null key in entry: null=" + value);
    } else if (value == null) {
      throw new NullPointerException("null value in entry: " + key + "=null");
    }
  }

On the other hand, I think you should use specialized rather than map... I'm pretty sure that such kind of type is giving headache to your team or other reader:

Map<String, List<Map<String, Map<String, Map<String, Map<String, String>>>>>>

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