Steps to reproduce

1. Log in to backoffice.
2. Go to Product catalog / Product types.
3. Create a new PT with name: 1New Product Type and identifier: 1new_product_type
4. From the command line execute: php bin/console ibexa:graphql:generate-schema
5. Open 1New Produc type in backoffice.

Actual result:

An error 500 occurs, cannot open PT.

The child config "values" under "overblog_graphql_types.ProductTypesList._enum_config" must be configured. 

Expected result:

Validation do not let user create PT with digit characters in name and identifier fields.

Note:
As workaround remove cache from project rm -rf var/cache/* and delete GraphQL from config folder from project directory.