fix: when triggers with input object and null as input value

lib/graphql/subscriptions.rb

@@ -250,6 +250,8 @@ def broadcastable?(query_str, **query_options)
     def normalize_arguments(event_name, arg_owner, args, context)
       case arg_owner
       when GraphQL::Schema::Field, Class
+        return args if args.nil?
+
         if arg_owner.is_a?(Class) && !arg_owner.kind.input_object?
           # it's a type, but not an input object
           return args

spec/graphql/subscriptions_spec.rb

@@ -1143,5 +1143,22 @@ class Schema < GraphQL::Schema
       assert_equal(':mySubscription:input:innerInput:', write_subscription_events[0].topic)
       assert_equal(':mySubscription:input:innerInput:', execute_all_events[0].topic)
     end
+
+    it 'correctly generates subscription topics when triggering with nil as input value' do
+      query_str = <<-GRAPHQL
+        subscription ($input: OuterInput) {
+          mySubscription (input: $input) {
+            fullName
+          }
+        }
+      GRAPHQL
+
+      schema.execute(query_str, variables: { 'input' => nil })
+
+      schema.subscriptions.trigger(:mySubscription, { 'input' => nil }, nil)
+
+      assert_equal(':mySubscription:input:', write_subscription_events[0].topic)
+      assert_equal(':mySubscription:input:', execute_all_events[0].topic)
+    end
   end
 end