CodeWriter should complain when asked to append a null String
Generally it is counter intuitive to append to the CodeWriter a code piece (a String) which is null, and having the CodeWriter silently ignore it.
Basically because in this way it makes more difficult (and weak, because just dependant on String names identifying code pieces) to follow the code piece flow and correct assemblage of them.
The proposal is to have CodeWriter thrown an exception instead. In this way one can figure out if either the code piece passed is null because the code piece identifier used is misspelled, or if there is a task dependency missing.