Merge pull request #1387 from sauliusg/patch1

Use #presence when fetching field's value.

app/views/rails_admin/main/show.html.haml

@@ -1,6 +1,6 @@
 - @model_config.show.with(:object => @object, :view => self).visible_groups.each do |fieldset|
   - unless (fields = fieldset.with(:object => @object, :view => self, :controller => self.controller).visible_fields).empty?
-    - if !(values = fields.map{ |f| v = f.value; (!v.nil? && v != '' && v != []) ? v : nil }).compact.empty? || !RailsAdmin::config.compact_show_view
+    - if !(values = fields.map{ |f| f.value.presence }).compact.empty? || !RailsAdmin::config.compact_show_view
       .fieldset
         %h4
           = fieldset.label