It is not necessary on the trial for the defendant to admit, nor for the plaintiff to prove lease, entry and ouster, or either of them, except in actions by one or more tenants in common, or joint tenants against their co-tenants; but this section shall not be construed to impair, nor in any way to affect, any of the rules of evidence now in force in regard to the maintenance and defense of the action.
735 ILCS 5/6-120