What happens if `childFieldName` is missing in `@denorm` annotation

In following example, only parentFieldName is specified and childFieldName is missing.

@denorm(sources=[DenormSource(source = TypeRef(typeName = 'MyType'), parentFieldName = 'parent')], strictHierarchy=true)
entity type MyTypetHierarchyDenorm mixes HierarchyDenorm<MyType> schema name 'STRUCT_MYTYPE'

Will childFieldName use id field by default? Or it won’t generate any MyTypetHierarchyDenorm data (except for root ones) if childFieldName is missing?

I did experiment and my observation is that MyTypetHierarchyDenorm data won’t be generated except for root ones, and that is probably due to missing of childFieldName field?