Rails 1.2 and RVM -- .irbrc fails with nil.[]= at line 51? -

when running rails 1.2 app rvm, in console log:

load error: /users/joe/.rvm/rubies/ruby-1.8.7-p302/.irbrc nomethoderror: have nil object when didn't expect it! might have expected instance of array. error occurred while evaluating nil.[]=     /users/joe/.rvm/scripts/irbrc.rb:51 

i'd clear error if can, make sure it's not impacting application.

i tried google , searching on stackoverflow first!