?? NonNullMetadata

??????:
Metadata
???????:
BeanMetadata, CollectionMetadata, ComponentMetadata, IdRefMetadata, MapMetadata, PropsMetadata, ReferenceListMetadata, ReferenceMetadata, RefMetadata, ServiceMetadata, ServiceReferenceMetadata, Target, ValueMetadata

@ConsumerType public interface NonNullMetadata extends Metadata
Metadata for a value that cannot null. All Metadata subtypes extend this type except for NullMetadata.

This Metadata type is used for keys in Maps because they cannot be null.