Using in vars initializers you can simply find. For example this code threw exception on runtime:

<?xml version="1.0"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" creationComplete="init()">
    <mx:Script><![CDATA[
        public var initialText: String = Application.application.parameters.initialText;

        private function init(): void {
           myText.text = initialText;
        }
    ]]></mx:Script>
    <mx:TextInput id="myText"/>
</mx:Application>

Environment: Flex SDK 3.3