Everyone has the right not to be arbitrarily arrested or detained.
Section 22: NZ Bill of Rights
Liberty of the person is about not being locked up without good reason. No one can be detained arbitrarily. This means police, and every other government official, must have a lawful reason to arrest or detain someone.
If the State locks you up, it must have a lawful reason and follow fair process. Random arrests or prolonged detention without trial are not allowed. You cannot be imprisoned just because someone dislikes you or because of your political views.