56 Ill. 2d at 116. Thus, on the one hand a tax refund was claimed by the plaintiffs because they paid the tax, and on the other hand by the intervenors, who asserted that they bore the actual burden of the tax. The Illinois Supreme Court found that a threshold issue was whether the plaintiffs, in order to establish their right to a refund, must show that they bore the burden of the tax. If neither party was entitled to a refund, the court reasoned that it would be unnecessary to review the constitutional validity of the tax. Consolidated, 56 Ill. 2d at 116. The court found that Illinois law recognized a general policy against unjust enrichment through the refund of illegal taxes and cited its decision in Benzoline Motor Fuel Co. v. Bollinger, 353 Ill. 600, 187 N.E. 657 (1933) (<HOLDING>). The court also examined the statutory policy
holding that defendants failure to assert the defense in any pretrial motions did not waive defendants limitations defense because the assertion of a limitations defense in the answer preserved defendants right to raise the defense both during the first trial and before the second holding that trial error in a civil case which went to the very heart of the defendants defense and was central to his defense could not be deemed harmless in the absence of any steps by the district court to mitigate the effects of the error holding that the running of the statute of limitations is an affirmative defense recognizing the legitimacy of a passon defense in the absence of any statute recognizing there is no authority to proceed against unknown persons in the absence of statute