I don't understand what "Nul" is. Is it the  'Nul' literal string? Is it some representation of undef — and are you use-ing warnings (and strict) at the start of your program? Is it something else I haven't imagined? (Update: I know the title of the OP includes the word "character," which implies \0, but still...) Can you please elaborate (preferably in the form of an SSCCE)?