You could avoid the `if` statements by simply declaring the `UserOptions` instance in the builder directly, and modifying that:
```
public Builder {
  private final UserOptions options = new UserOptions();

  public Builder page(int page) {
    options.queryParameters.put("page", String.valueOf(page));
    return this;
  }
  ...
  public UserOptions build() {
    return options;
  }
}
```