Remove the unwanted #empty call on the collection (#524)

lib/jbuilder/jbuilder_template.rb

@@ -141,9 +141,7 @@ def _render_partial_with_options(options)
     options.reverse_merge! ::JbuilderTemplate.template_lookup_options
     as = options[:as]
 
-    if options.key?(:collection) && (options[:collection].nil? || options[:collection].empty?)
-      array!
-    elsif as && options.key?(:collection) && CollectionRenderer.supported?
+    if as && options.key?(:collection) && CollectionRenderer.supported?
       collection = options.delete(:collection) || []
       partial = options.delete(:partial)
       options[:locals].merge!(json: self)
@@ -156,9 +154,11 @@ def _render_partial_with_options(options)
         raise ::NotImplementedError, "The `:spacer_template' option is not supported in collection rendering."
       end
 
-      CollectionRenderer
+      results = CollectionRenderer
         .new(@context.lookup_context, options) { |&block| _scope(&block) }
         .render_collection_with_partial(collection, partial, @context, nil)
+
+      array! if results.respond_to?(:body) && results.body.nil?
     elsif as && options.key?(:collection) && !CollectionRenderer.supported?
       # For Rails <= 5.2:
       as = as.to_sym

test/jbuilder_template_test.rb

@@ -291,6 +291,22 @@ class JbuilderTemplateTest < ActiveSupport::TestCase
       assert_equal [], result
     end
 
+    test "works with an enumerable object" do
+      enumerable_class = Class.new do
+        include Enumerable
+        alias length count # Rails 6.1 requires this.
+
+        def each(&block)
+          [].each(&block)
+        end
+      end
+
+      result = render('json.array! @posts, partial: "post", as: :post, cached: true', posts: enumerable_class.new)
+
+      # Do not use #assert_empty as it is important to ensure that the type of the JSON result is an array.
+      assert_equal [], result
+    end
+
     test "supports the cached: true option" do
       result = render('json.array! @posts, partial: "post", as: :post, cached: true', posts: POSTS)
 
@@ -317,7 +333,7 @@ class JbuilderTemplateTest < ActiveSupport::TestCase
       assert_equal "Heinemeier Hansson", result[2]["author"]["last_name"]
       assert_equal "Pavel", result[5]["author"]["first_name"]
     end
-    
+
     test "supports the cached: ->() {} option" do
       result = render('json.array! @posts, partial: "post", as: :post, cached: ->(post) { [post, "foo"] }', posts: POSTS)