Index: vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
===================================================================
--- vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb	(revision 9082)
+++ vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb	(working copy)
@@ -281,7 +281,14 @@
 
       def add_column_options!(sql, options) #:nodoc:
         sql << " DEFAULT #{quote(options[:default], options[:column])}" if options_include_default?(options)
-        sql << " NOT NULL" if options[:null] == false
+        # must explcitly check for :null to allow change_column to work on migrations
+        if options.has_key? :null
+          if options[:null] == false
+            sql << " NOT NULL"
+          else
+            sql << " NULL"
+          end
+        end
       end
 
       # SELECT DISTINCT clause for a given set of columns and a given ORDER BY clause.