The EmptySrcAttributeFilter checks if an empty src attribute is found in the response.
Empty src attribute is problematic as it makes some browsers, i.e. firefox, request an URL twice.
Two issues arise:
1. Unnecessary server load.
2. If the browser only renders the first response, some links in the page might be broken as
wicket rerendered them in the second request and dropped the ones rendered in the first request.
Filters the response buffer and returns the filtered response that can be used in the next
filter or returned to the real output itself.
A filter may alter the response buffer and return the response buffer itself.