spring boot field is always null

Question

In my Spring BOOT application, I have a User class and a LoginCreadential class.

In my User class, I have:

@OneToOne(fetch = FetchType.LAZY,targetEntity = LoginCredential.class)
@JoinColumn(name = "userID",referencedColumnName = "userID")
@JsonIgnore
private LoginCredential loginCredential;

And in my LoginCraedential class:

@OneToOne(mappedBy = "loginCredential", fetch = FetchType.LAZY)
User user;

And when I am creating LoginCreadential through my React.js application like this :

    var xhr = new XMLHttpRequest();
    xhr.open('POST', 'http://localhost:8080/login/');
    xhr.setRequestHeader("Content-Type", "application/json");
    xhr.send(JSON.stringify({ email: this.state.email,passwordHash:this.state.passwordHash }));

I get something like this :

{"userID":65,"passwordHash":"sad","user":null,"email":"aszzzzzzzzzzdasdasd"},

My LoginCreadential class has two constructors:

LoginCredential()
{

}
public LoginCredential(String eMail, String passwordHash,User user)
{
    this.eMail=eMail;
    this.passwordHash=passwordHash;
    this.user=user;
}

In my LoginCredentialController class, I have :

@PostMapping("/login")
void newLoginCredential(@RequestBody LoginCredential newLoginCredential)
{
    List<LoginCredential> userList=repository.findByEmailAddress(newLoginCredential.getEMail());
    if(userList==null || userList.size()==0)
        repository.save(newLoginCredential);
}

The user is always null, shouldn't it create an empty User or something like this ?

If not how can I achieve it?