Springboot ExampleMatcher always returns no result - spring-boot

Question

I have the following entity and I'm trying to use ExampleMatcher for simple queries:
#Entity(name="UserAccount")
#Table(name = "useraccount", catalog = "useraccount")
#Data
public class UserAccount implements Serializable
{
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Column(nullable = false, unique = true)
private String username;
#Column(nullable = false, unique = true)
private String mail;
private String password;
private boolean isEnabled;
private Timestamp credentialExpire;
private boolean isAccountNonLocked;
private boolean isSuspended;
private Timestamp accountExpire;
#ManyToMany(cascade = {CascadeType.DETACH, CascadeType.MERGE, CascadeType.REFRESH}, fetch=FetchType.LAZY)
#JoinTable(name = "user_to_privileges", catalog = "useraccount",
joinColumns = {#JoinColumn(name = "user_id", referencedColumnName = "id", nullable = false)},
inverseJoinColumns = {#JoinColumn(name = "privilege_id", referencedColumnName = "id", nullable = false)})
private Set<Privilege> privileges= new HashSet<>();
#ManyToMany(cascade = {CascadeType.DETACH, CascadeType.MERGE, CascadeType.REFRESH}, fetch=FetchType.LAZY)
#JoinTable(name = "user_to_organizations", catalog = "useraccount",
joinColumns = {#JoinColumn(name = "user_id", referencedColumnName = "id", nullable = false)},
inverseJoinColumns = {#JoinColumn(name = "organization_id", referencedColumnName = "id", nullable = false)})
private Set<Organization> organizations= new HashSet<>();
#OneToOne(mappedBy ="user", cascade = {CascadeType.REMOVE, CascadeType.MERGE, CascadeType.REFRESH}, fetch=FetchType.LAZY)
#PrimaryKeyJoinColumn
#Setter(AccessLevel.NONE)
private UserRegister register;
#OneToMany(mappedBy ="tokenId.user", cascade = {CascadeType.REMOVE, CascadeType.MERGE, CascadeType.REFRESH}, fetch=FetchType.LAZY)
private Set<SecureToken> tokens = new HashSet<>();
#OneToOne(mappedBy ="user", cascade = {CascadeType.REMOVE, CascadeType.MERGE, CascadeType.REFRESH}, fetch=FetchType.LAZY)
#PrimaryKeyJoinColumn
private UserLogin login;
//all the methods omitted from brevity
}
I create the Example matcher as follows:
UserAccount account= new UserAccount();
account.setUsername("John");
ExampleMatcher matcher = ExampleMatcher.matching()
.withIgnoreCase()
.withStringMatcher(ExampleMatcher.StringMatcher.CONTAINING);
Example<UserAccount> regExample = Example.of(account, matcher);
List<UserAccount> out = repository.findAll(regExample);
Consider that a user with username "John" exists, but the output is always empty, no matter what parameter I fill.
Edit: this helps to find the solution: Are there any possible ways to ignore all paths of JPA Example Matcher. There is no way to automatically ignore primitive fields when not used?
Edit: Notice that I want to find all the UserAccount containing the specified strings in the selected fields. With other entities the configuration of ExampleMatcher works.