Is it mandatory to instantiate collection fields in JPA?

Question

I read an article in which the author implemented the Entity class as follows:

@Entity
public class Product {

 @OneToMany
 private List<Part> parts; // note the missing "= new ArrayList<Part>();"

 public Product() {
 }

 // getters and setters

}

I always used to create instances of collection fields, in this case parts, either inline ( private List<Part> parts = new ArrayList<Part>();), or inside the constructor, since, as far as I remember, this did not lead to the appearance of all kinds of NPE.

I thought that everything changed in JPA 2 and now JPA runtime automatically creates a field using enhancement or reflection of bytecode at runtime, so I gave it another try, however I still can not get it to work without instantiating partsotherwise it aProduct.getParts().add(aPart)will cause NPE.

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Answer 1

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Answer 2

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