Hello I have this problem while installing many of the gems on my Debian 6 (upped to date).
# gem install activemodel
ERROR: While executing gem ... (NoMethodError)
undefined method `call' for nil:NilClass
# ruby -v
ruby 1.8.7 (2010-08-16 patchlevel 302) [i486-linux]
# gem -v
1.3.7
# gem list
*** LOCAL GEMS ***
activesupport (3.2.0)
builder (3.0.0)
diff-lcs (1.1.3)
i18n (0.6.0)
multi_json (1.0.4)
rake (0.9.2.2)
rspec (2.8.0)
rspec-core (2.8.0)
rspec-expectations (2.8.0)
rspec-mocks (2.8.0)
xmpp4r (0.5)