Exposure of nil to end-users

[Ben Harper <rogojin@...>]

I am using Lua as a language that allows end-users to manipulate
database records.
My problem is that I'm not sure how to expose NULL values to the user.

In this example, value = nil
User Types:      value .. "abc"
User Expects:   'abc'
User Gets:        Error: attempt to concatenate a nil value

Has anybody had a similar problem, and how have you dealt with it?

Thanks,
Ben