Fixed or removed about 25 broken links

Information about the links that were removed because I could not find a replacement :
* removed links to comprehension page as the comprehension page does not exist anymore in the reference doc.
* removed links to nullsafe-lookup  (actually completely removed the text about nullsafe-lookup)
* removed links to catch and finally that do not exists anymore in the reference doc.
* removed links to class-instantiation that does not exists anymore in the reference doc.