I am here to ask quick question about builder and optionals. I have this simple example here:

public class User {  private final String name; private final String lastname; private final String phone;  private User(Builder builder) {     this.name = builder.name;     this.lastname = builder.lastname;     this.phone = builder.phone; }  public String getName() {     return name; }  public String getLastname() {     return lastname; }  public String getPhone() {     return phone; }  @Override public String toString() {     return "User{" +             "name='" + name + '\'' +             ", lastname='" + lastname + '\'' +             ", phone='" + phone + '\'' +             '}'; }  public static class Builder {     private String name;     private String lastname;     private String phone = "";      public Builder(String name, String lastname) {         name(name);         lastname(lastname);     }      private Builder name(String name) {         this.name = Optional.ofNullable(name).orElseThrow(() -> new IllegalArgumentException("Name must not be null"));         return this;     }      private Builder lastname(String lastname) {         this.lastname = Optional.ofNullable(lastname).orElseThrow(() -> new IllegalArgumentException("Last name must not be null"));         return this;     }      public Builder phone(String phone) {         this.phone = Optional.ofNullable(phone).orElse("");         return this;     }      public User build() {         return new User(this);     }  } 

}

So.. this code work as expected but I have some doubts. My question is about private methods in builder(name and lastname). Is it allowed in a world of a clean code? And also about this Optionals, are they well written? I just start using this functionality so I don’t know for sure if I am right here.