Rewrite continues:

Rewrite continues:
- EmptyVariableException can be easily replaced by InvalidArgumentException (IEA)
  because there is no need for to over-detailed exceptions, but still it is a
  good idea to have more (custom) around than the defaults
- MissingMethodException was no longer used and is now emptied
- updated TODOs.txt
- ignored vendor in todo-builder.sh

Signed-off-by: Roland Häder <roland@mxchange.org>