             print("Tried to uppercase a null string")
             throw ExecErrors.NullPointerError
         }
-        set(variable, value: get(variable)!.uppercaseString)
+        try set(variable, value: get(variable)!.uppercaseString)
         return nil
     }
     

        methods["blackAndWhite"] = blackAndWhite
        methods["toLower"] = toLower
        methods["toUpper"] = toUpper
        methods["toCap"] = toUpper
        // MARK: parse
        var commands: [(Int, String)] = []
        for line in 0..<lines.count {

    }
    
    func getBaloons() -> [(UIImage, UIImage, UIImage)] {
        return baloons
    }
    
    func getImage(variable: String) -> UIImage {
