Empty contenttype groups will result in 500 error in frontend.
Step to reproduce:
1. Create a ContentType group with following name: MYGROUP
2. Create Schema with ezplatform:graphql:generate-schema
3. Try to access to the application domain

Error:

 InvalidConfigurationException
The child node "fields" at path "overblog_graphql_types.DomainGroup*MYGROUP*Types._object_config" must be configured.

MYGROUP: The ContentTypeGroup name created in 1

Below Files must not be created if the ContentType Group is empty

Written app/config/graphql/ezplatform/DomainGroupMYGROUP.types.yml
Written app/config/graphql/ezplatform/DomainGroupMYGROUPTypes.types.yml