Fixes identifier errors.

app/models/identifier/guid.rb

@@ -1,4 +1,3 @@
 class Identifier::Guid < Identifier 
-
-
+  validates :namespace_id, absence: true
 end

app/models/identifier/local_id.rb

@@ -1,2 +1,4 @@
 class Identifier::LocalId < Identifier 
+  belongs_to :namespace
+  validates :namespace, presence: true
 end

spec/models/identifier/guid_spec.rb

@@ -11,10 +11,10 @@
     end
   end
 
-  specify 'namespace is nil' do
-    guid_identifier.namespace = FactoryGirl.build(:valid_namespace)
+  specify 'namespace_id is nil' do
+    guid_identifier.namespace_id = FactoryGirl.create(:valid_namespace).id
     guid_identifier.valid?
-    expect(guid_identifier.errors.include?(:namespace)).to be_true
+    expect(guid_identifier.errors.include?(:namespace_id)).to be_true
   end
 
 end