* fix bug in earliest cohort code

admin/Gemfile

@@ -41,7 +41,7 @@ gem 'uuidtools', '2.1.2'
 gem 'jquery-rails' # , '2.3.0' # pinned because jquery-ui-rails was split from jquery-rails, but activeadmin doesn't support this gem yet
 gem 'jquery-ui-rails', '4.2.1'
 gem 'rails3-jquery-autocomplete'
-gem 'activeadmin', github: 'activeadmin', branch: '0-6-stable'
+gem 'activeadmin' #, github: 'activeadmin', branch: '0-6-stable'
 gem 'mime-types', '1.25'
 gem 'meta_search'
 gem 'fog',  "~> 1.18.0"

admin/app/models/cohort.rb

@@ -56,7 +56,8 @@ class Cohort < ActiveRecord::Base
 
   def self.earliest_cohort
     starting = User.where(admin: false).order(:created_at).first.created_at
-    starting = EARLIEST_DATE if starting < EARLIEST_DATE
+    starting = EARLIEST_DATE if starting.nil? || starting < EARLIEST_DATE
+    starting # this is necessary to always return not null
   end
 
   def self.cohort_group_ranges(starting=nil, ending=nil)