ManyToMany Correct implementation

Hi All,
I’m using Hibernate a lot in my new project and combine it with QueryDSL which I started implementing instead of native SQL queries which became cumbersome and hard to maintain.
The biggest knowledge gap I have is how to properly map relations in my project, ManyToMany in particular.
I’ve read the article Vlad posted (thank you for your hard work it is a lifesaver), about proper handling this relational type.
However, I have a helper class which I use in my integration test which constructs entities at the repository level (so I can test all layers of my code) and when I use the above add method I get an NPE exception which indicates that the initialization of my classes property (one side of the relation) wasn’t initialized. Here is the code block:

private Entity create(Long accountId, String name, Set<AnotherEntity> others) {
        var entity = Entity.builder()
        other.forEach(entity::addOther); -> NPE
        return entity;

Here is how the relations are organized:

     /* Inside Entity class */
    @ManyToMany(cascade = {
    @JoinTable(name = "entity_other",
            joinColumns = @JoinColumn(name = "entity_id"),
            inverseJoinColumns = @JoinColumn(name = "other_id")
    private Set<OtherEntity> others = new HashSet<>();

    public void addOther(OtherEntity other) {
        others.add(other); // NPE like others wasn't initialized to new HashSet<>()

   /* Inside Other class */
    @ManyToMany(mappedBy = "others")
    private Set<Entity> entities = new HashSet<>();

I’ve just changed names for the purpose of hiding the business logic.
I’m wondering do we need to implement manipulations with the repository in a thin layer that we can call the Service layer or OtherCrud.class which should provide us access to the repository and escape usage of the repository outside of the above-mentioned service class in general.
Also if there are some useful things to note about the relationship please let me know.
Thank you very much in advance.

So the issue was in using the Builder by Lombok which generates a null value upon initialization.
Does this mean that when providing a “creator” for e.g. Other you should not have a setter for that entity since it can only be added through Entity class and the add method?

you should use something like if you are using lombok

private Set others = new HashSet<>();

I managed to make this work and relation is saved from parent side of the relationship.
However when I try to use the Repository of the child (child was modified so it still has eager loading ManyToOne) to see does the child contain parent it doesn’t persist the parent.

I can’t wrap my head around this, can you guys help?