diff --git a/app/helpers/categories_helper.rb b/app/helpers/categories_helper.rb
index 4454141..d6aea24 100644
--- a/app/helpers/categories_helper.rb
+++ b/app/helpers/categories_helper.rb
@@ -12,7 +12,7 @@ module CategoriesHelper
   end
 
   def category_color_style(category)
-    return '' if category.display_color.blank?
+    return '' if category.nil? or category.display_color.blank?
     'background-color: #'+category.display_color+';'
   end
 
diff --git a/test/unit/categories_helper_test.rb b/test/unit/categories_helper_test.rb
index e8fed85..768e235 100644
--- a/test/unit/categories_helper_test.rb
+++ b/test/unit/categories_helper_test.rb
@@ -31,4 +31,10 @@ class CategoriesHelperTest < ActiveSupport::TestCase
     assert_equal '', category_color_style(category2)
   end
 
+  should 'not return category parent color if category is nil' do
+    assert_nothing_raised do
+      assert_equal '', category_color_style(nil)
+    end
+  end
+
 end
--
libgit2 0.21.2