object needs to respond to select instead of being an enumerable

lib/jekyll/filters.rb

@@ -233,11 +233,11 @@ module Jekyll
     #
     # Returns the filtered array of objects
     def where(input, property, value)
-      return input unless input.is_a?(Enumerable)
+      return input unless input.respond_to?(:select)
       input = input.values if input.is_a?(Hash)
       input.select do |object|
         Array(item_property(object, property)).map(&:to_s).include?(value.to_s)
-      end
+      end || []
     end
 
     # Filters an array of objects against an expression
@@ -248,7 +248,7 @@ module Jekyll
     #
     # Returns the filtered array of objects
     def where_exp(input, variable, expression)
-      return input unless input.is_a?(Enumerable)
+      return input unless input.respond_to?(:select)
       input = input.values if input.is_a?(Hash) # FIXME
 
       condition = parse_condition(expression)
@@ -257,7 +257,7 @@ module Jekyll
           @context[variable] = object
           condition.evaluate(@context)
         end
-      end
+      end || []
     end
 
     # Sort an array of objects

test/test_filters.rb

@@ -15,6 +15,10 @@ class TestFilters < JekyllUnitTest
     end
   end
 
+  class SelectDummy
+    def select; end
+  end
+
   context "filters" do
     setup do
       @filter = JekyllFilter.new({
@@ -530,6 +534,11 @@ class TestFilters < JekyllUnitTest
         assert_equal 1, results.length
         assert_equal 4.7, results[0]["rating"]
       end
+
+      should "always return an array if the object responds to `select`" do
+        results = @filter.where(SelectDummy.new, "obj", "1 == 1")
+        assert_equal [], results
+      end
     end
 
     context "where_exp filter" do
@@ -602,6 +611,11 @@ class TestFilters < JekyllUnitTest
         assert_equal 1, results.length
         assert_equal site.posts.find { |p| p.title == "Foo Bar" }, results.first
       end
+
+      should "always return an array if the object responds to `select`" do
+        results = @filter.where_exp(SelectDummy.new, "obj", "1 == 1")
+        assert_equal [], results
+      end
     end
 
     context "sort filter" do