(a) The party brought before any court or judge, by virtue of any writ of habeas corpus, may deny the material facts set forth in the return, or allege any fact to show either that his or her detention or imprisonment is unlawful, or that he or she is entitled to his or her discharge. The allegations or denials shall be on oath.
(b) The return and the allegations made against it may be amended, by leave of the court or judge before whom the writ is returned at any time, that thereby material facts may be ascertained.