Java 17: Stream API Collectors.groupingBy returns null values in nested collections
I'm having trouble with Hey everyone, I'm running into an issue that's driving me crazy. I'm currently working with Java 17 and trying to group a list of objects using the `Stream API` with `Collectors.groupingBy()`. However, I'm encountering a problem where some of the grouped results contain null values, which is not the expected behavior. My object structure consists of a `Person` class with fields like `id`, `name`, and `age`, and I'm trying to group them by `age`. Here's the code I'm using: ```java import java.util.*; import java.util.stream.*; class Person { private int id; private String name; private Integer age; // Using Integer to allow null // Constructor, getters, and setters public Person(int id, String name, Integer age) { this.id = id; this.name = name; this.age = age; } public Integer getAge() { return age; } } public class Main { public static void main(String[] args) { List<Person> people = Arrays.asList( new Person(1, "Alice", 30), new Person(2, "Bob", null), // This person has a null age new Person(3, "Charlie", 30), new Person(4, "David", 25) ); Map<Integer, List<Person>> groupedByAge = people.stream() .collect(Collectors.groupingBy(Person::getAge)); System.out.println(groupedByAge); } } ``` When I run this code, I see output like this: ```plaintext {25=[Person@1b6d3586], 30=[Person@6d06d69c], null=[Person@7852e922]} ``` I expected the result to ignore null values when grouping. I’ve tried filtering out null ages before grouping like this: ```java Map<Integer, List<Person>> groupedByAge = people.stream() .filter(person -> person.getAge() != null) .collect(Collectors.groupingBy(Person::getAge)); ``` But I still see the `null` key in the final map. I would like to know if there's a better way to handle this scenario or if I'm missing something in my approach. Any advice would be greatly appreciated! I'm working on a CLI tool that needs to handle this. Am I missing something obvious? I'm working with Java in a Docker container on Windows 10. Could this be a known issue? This is happening in both development and production on Ubuntu 22.04. Thanks in advance! I'm using Java 3.11 in this project. Thanks, I really appreciate it!