Where a defendant has previously been convicted of a felony under a statute later found to be unconstitutional, it may still serve as the predicate conviction for a charge of unlawful use of a weapon by a felon unless he has, prior to his arrest, petitioned the court to vacate it.The 1st District Appellate Court affirmed the decision of Cook County Circuit Judge Frank G. Zelezinski.Keshawn Carter had previously been convicted of aggravated unlawful use of a weapon in 2008. On June 2, 2012, four police officers entered …