Check for the key instead of the value, because it (the value) can be false.

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@3322 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -298,7 +298,7 @@ module ActiveRecord
       def add_column(table_name, column_name, type, options = {})
         native_type = native_database_types[type]
         sql_commands = ["ALTER TABLE #{table_name} ADD #{column_name} #{type_to_sql(type, options[:limit])}"]
-        if options[:default]
+        if options.has_key?(:default)
           sql_commands << "ALTER TABLE #{table_name} ALTER #{column_name} SET DEFAULT '#{options[:default]}'"
         end
         if options[:null] == false