I am moving this question to AEM Forums (the current forums where you have posted the question is for DTM).
AppSpider is 3rd party Security testing web application. I guess, the string "aaaa..." is one of the pre-build test case which this application is applying to your custom component and your component is not able to handle it (Exception handling missing). I would request you to refer the documentation of this application to better understand the error message or you may contact their support for it.
If my understanding about this question is wrong please correct me in it.