Make input non null for processors

[jangalinski]

There are cases, where we do not have an input loop variable for a processor. Example: a processor on FilsPecBuilder that is resonsible for some copyright notes or file-level annotations does not have a loop variable. But it proved to be a bad idea that we work with nullable types all the time for all processors.

Fix: remove nullable, provide NULL-INPUT type and define a processor that supports this NULL-INPUT.