Merge pull request #3520 from delftswa2014/sort-null

lib/jekyll/filters.rb

@@ -222,6 +222,9 @@ module Jekyll
     #
     # Returns the filtered array of objects
     def sort(input, property = nil, nils = "first")
+      if input.nil?
+          raise ArgumentError.new("Cannot sort a null object.")
+      end
       if property.nil?
         input.sort
       else

test/test_filters.rb

@@ -280,6 +280,12 @@ class TestFilters < JekyllUnitTest
     end
 
     context "sort filter" do
+      should "raise Exception when input is nil" do
+        err = assert_raises ArgumentError do
+          @filter.sort(nil)
+        end
+        assert_equal "Cannot sort a null object.", err.message
+      end
       should "return sorted numbers" do
         assert_equal [1, 2, 2.2, 3], @filter.sort([3, 2.2, 2, 1])
       end