Changing the way nil works

["paulmatthews" <paulmatthews@...>]

G'Day,

I want to change the way nil works. In particular:
  number + nil       -> nil    #not error
  nil + number       -> nil    #not error
  ...etc...
  string .. nil      -> nil    #not error
  nul .. string      -> nil    #not error
  ...etc...

That is nil works sort of like NaN, everything it touches changes to 
nil also. What best (fastest run time) way to achieve this.

--
Paul Matthews