database_authenticatable_default_option.diff

diff --git a/lib/devise/schema.rb b/lib/devise/schema.rb
index f0ff2a1..94296e4 100644
--- a/lib/devise/schema.rb
+++ b/lib/devise/schema.rb
@@ -14,7 +14,7 @@ module Devise
     # encrypter password field in 128 characters.
     def database_authenticatable(options={})
       null    = options[:null] || false
-      default = options[:default] || ""
+      default = options[:default] || null ? nil : ""
 
       apply_devise_schema :email,              String, :null => null, :default => default
       apply_devise_schema :encrypted_password, String, :null => null, :default => default, :limit => 128