Filter nil values from include param

(cherry picked from commit 4b93707)

Author: hidde-jan

lib/jsonapi/request_parser.rb

@@ -226,7 +226,7 @@ def parse_include_directives(raw_include)
 
       return if included_resources.empty?
 
-      result = included_resources.map do |included_resource|
+      result = included_resources.compact.map do |included_resource|
         check_include(@resource_klass, included_resource.partition('.'))
         unformat_key(included_resource).to_s
       end

test/controllers/controller_test.rb

@@ -3642,6 +3642,11 @@ def test_complex_includes_base
     assert_response :success
   end
 
+  def test_complex_includes_filters_nil_includes
+    assert_cacheable_get :index, params: {include: ',,'}
+    assert_response :success
+  end
+
   def test_complex_includes_two_level
     assert_cacheable_get :index, params: {include: 'things,things.user'}