If you make the Rails application as a proxy to other web application, you often meet problems with parameters: "TypeError: expected Hash (got String) for param ". If you want to make Rails(Rack) to ignore these errors, this code helps. Put this in RAILS_ROOT/initializers folder. My environemnt is Ruby 2.0.0p247 + Rails 3.2.12 + Rack 1.4.5.

Rails_ignore_normalize_params_TypeError_expected_Hash_for_param.rb

module Rack::Utils
  # to avoid this error:
  #  home/rack-1.4.5/lib/rack/utils.rb  line 127 
  #  raise TypeError, "expected Hash (got #{params[k].class.name}) for param `#{k}'" unless params_hash_type?(params[k])
  unless defined? normalize_params_without_error_passthru
    alias normalize_params_without_error_passthru normalize_params
    module_function :normalize_params_without_error_passthru
  end
  
  def normalize_params(params, *args)
    begin
      normalize_params_without_error_passthru(params, *args)
    rescue
      STDERR.puts "[warn] Rack::Utils::normalize_params failed: #{$!}"
      return params
    end
  end
  module_function :normalize_params
end