fix railsadminteam#1425 datetime field value disappears in forms

lib/rails_admin/config/fields/types/datetime.rb

@@ -52,7 +52,7 @@ def parse_date_string(date_string)
           end
 
           def formatted_date_value
-            value = bindings[:object].new_record? && self.value.nil? && !self.default_value.nil? ? self.default_value : nil
+            value = bindings[:object].new_record? && self.value.nil? && !self.default_value.nil? ? self.default_value : self.value
             value.nil? ? "" : I18n.l(value, :format => localized_date_format).strip
           end
 

spec/rails_admin/config/fields/types/datetime_spec.rb

@@ -0,0 +1,18 @@
+require 'spec_helper'
+
+describe RailsAdmin::Config::Fields::Types::Datetime do
+  describe 'formatted_date_value' do
+    it 'gets object value' do
+      expect(RailsAdmin.config(FieldTest).fields.find{|f| f.name ==:datetime_field}.with(object: FieldTest.new(datetime_field: DateTime.parse('02/01/2012'))).formatted_date_value).to eq 'January 02, 2012'
+    end
+
+    it 'gets default value for new objects if value is nil' do
+      RailsAdmin.config(FieldTest) do |config|
+        field :datetime_field do
+          default_value DateTime.parse('01/01/2012')
+        end
+      end
+      expect(RailsAdmin.config(FieldTest).fields.find{|f| f.name ==:datetime_field}.with(object: FieldTest.new).formatted_date_value).to eq 'January 01, 2012'
+    end
+  end
+end