Fix uniqueness validation on localized nil fields

- Fix #4052

CHANGELOG.md

@@ -37,6 +37,8 @@ For instructions on upgrading to newer versions, visit
 
 * \#4091 Use sublcass context when calling a scope defined in a superclass. (Edgars Beigarts)
 
+* \#4052 Fixed uniqueness validation on localized fields with no value.
+
 * \#4005 Fixed inclusion of mongoid with Rails components that don't have the Rails environment.
 
 * \#3993 Fixes issue where `dup`/`clone` fails for embedded documents that use store_as without using Mongoid::Atributes::Dynamic

lib/mongoid/validatable/uniqueness.rb

@@ -122,8 +122,8 @@ def create_criteria(base, document, attribute, value)
       def criterion(document, attribute, value)
         field = document.database_field_name(attribute)
 
-        if localized?(document, field)
-          conditions = value.inject([]) { |acc, (k,v)| acc << { "#{field}.#{k}" => filter(v) } }
+        if value && localized?(document, field)
+          conditions = (value || {}).inject([]) { |acc, (k,v)| acc << { "#{field}.#{k}" => filter(v) }}
           selector = { "$or" => conditions }
         else
           selector = { field => filter(value) }

spec/mongoid/validatable/uniqueness_spec.rb

@@ -147,6 +147,35 @@
                 Dictionary.reset_callbacks(:validate)
               end
 
+              context "when no attribute is set" do
+
+                context "when no document with no value exists in the database" do
+
+                  let(:dictionary) do
+                    Dictionary.new
+                  end
+
+                  it "returns true" do
+                    expect(dictionary).to be_valid
+                  end
+                end
+
+                context "when a document with no value exists in the database" do
+
+                  before do
+                    Dictionary.create
+                  end
+
+                  let(:dictionary) do
+                    Dictionary.new
+                  end
+
+                  it "returns false" do
+                    expect(dictionary).to_not be_valid
+                  end
+                end
+              end
+
               context "when the attribute is unique" do
 
                 context "when single localization" do