java - NullPointerException on getting ManyToMany relation -


i got entity account manytomany entity role.

@entity public class account {      @id @generatedvalue(strategy=generationtype.sequence)     private long id;      @manytomany(cascade= {cascadetype.persist,cascadetype.merge,cascadetype.refresh}, fetch=fetchtype.eager)     @jointable(name="account_role")     private set<role> roles;      // getters, setters }

when try access relationship collection got nullpointerexception roles null:

account account = new account(); account.getroles().size();

shouldn't empty set injected roles? or default behaviour , should control roles creation by:

   private set<role> roles = new hashset()<>;

you created object

account account = new account();

that wasn't managed jpa. how expect not null?

reference type instance variables are, default, assigned null. set reference type. should create set (as you've suggested).

private set<role> roles = new hashset()<>;

or retrieve entity instance jpa entitymanager instance

account account = entitymanager.find(account.class, 42);

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