Attempt accessing only valid item properties

lib/jekyll/filters.rb

@@ -347,7 +347,7 @@ def item_property(item, property)
       @item_property_cache[property][item] ||= begin
         if item.respond_to?(:to_liquid)
           property.to_s.split(".").reduce(item.to_liquid) do |subvalue, attribute|
-            parse_sort_input(subvalue[attribute])
+            parse_sort_input(access_property(subvalue, attribute))
           end
         elsif item.respond_to?(:data)
           parse_sort_input(item.data[property.to_s])
@@ -357,10 +357,19 @@ def item_property(item, property)
       end
     end
 
+    def access_property(object, key)
+      return object unless object.respond_to?(:[])
+
+      accessor = parse_sort_input(key)
+      return object if object.is_a?(Array) && !accessor.is_a?(Integer)
+
+      object[accessor]
+    end
+
     # return numeric values as numbers for proper sorting
     def parse_sort_input(property)
       number_like = %r!\A\s*-?(?:\d+\.?\d*|\.\d+)\s*\Z!
-      return property.to_f if property =~ number_like
+      return property.to_f if property.to_s =~ number_like
 
       property
     end

test/test_filters.rb

@@ -906,6 +906,16 @@ def to_liquid
         assert_equal 0, @filter.where(hash, "category", "ear").length
       end
 
+      should "not throw exception when an item is null" do
+        array = [{}, { "color" => "text" }, { "foo" => "bar" }, nil]
+        assert_equal [{ "color" => "text" }], @filter.where(array, "color", "text")
+      end
+
+      should "not throw exception when an item itself is an array" do
+        array = [{}, { "color" => "text" }, [], { "foo" => "bar" }]
+        assert_equal [{ "color" => "text" }], @filter.where(array, "color", "text")
+      end
+
       should "stringify during comparison for compatibility with liquid parsing" do
         hash = {
           "The Words" => { "rating" => 1.2, "featured" => false },