[ruby-talk:6642] Hash with a key of nil ?

While reading data in from a file and populating a hash, I accidentally 
added a key/val pair of nil/nil. All was fine until I tried to sort the 
hash and got "NameError: undefined method `<=>' for nil". I know I should 
check for nils before populating a hash, but it raises two questions in my 
mind:

1) Should nil be allowed as a Hash key? This does not make sense to me.
2) Maybe there should be a method defined for nil.<=> ? I think if it 
always returned -1 it would be appropriate.

-RPM

x={"a"=>1, nil=>nil} --> {nil=>nil, "a"=>1}
x                    --> {nil=>nil, "a"=>1}
x.keys               --> [nil, "a"]
x.values             --> [nil, 1]
x.sort               --> NameError: undefined method `<=>' for nil
                     --> `<=>'
                     --> `sort'
                     --> in `irb_binding'
-- 
Ross Mohn
[e-mail]