Custom exception handler no longer working with 8.1.0

[oliemansm]

Describe the bug
After upgrading from 8.0.0 to 8.1.0 the custom exceptions stopped working and all graphql errors are being converted back to the default "Internal server error" message.

To Reproduce
Steps to reproduce the behavior:

1. Expose a bean with @ExceptionHandler methods to create GraphQLError in case of certain exceptions
2. Configure graphql.servlet.exception-handlers-enabled: true
3. Run a GraphQL query which should result in an exception
4. The returned error always contain a default message starting with "Internal server error"

Expected behavior
Instead of the default GraphQLError I'd expect my custom error to be returned.