Action return type for nullable scalar is non-nullable

### Version Information

Server Version: v2.22.0

### Environment

OSS

### What is the current behaviour?

Action with nullable **scalar** return type has non-nullable return type in schema. It's only bad for scalar return types, it's fine for objects.

### What is the expected behaviour?

Action with a nullable scalar return type should have a nullable return type in the schema.

### How to reproduce the issue?

1. create action with nullable scalar return type

### Screenshots or Screencast

Action definition:

In schema: