This is unnecessary, leaving it out leaves plenty enough information.

lex() returning NULL is used to convey an error case but having not allocated
any tokens in the case of an empty input file isn't an error case. This patch
causes lex to treat an empty token stream after successfully examining a file
as just a single EOL token. This is a fair approximation of an empty file for
this assembler's purposes, and results in the correct behaviour of an empty
output file.

This emulator provides a rough way for binaries designed for this CPU to be
executed in a virtual/emulated CPU for testing purposes. This patch also adds
a small test setup for automated assembly, execution and checking of register
postconditions for programs.