Just curious: Why is tonumber(nil) not 0?

[Mike Crowe <drmikecrowe@...>]

Hi folks,

I was briefly caught by doing this test:

   if tonumber(something) > 0 then
      ...
   end

with something=nil. 

I'm not advocating a change, but what's the thought-process behind this 
behavior?  Wouldn't you consider the numeric value of nil to be 0?

Mike