@ajeet I am sorry for not elaborating on my point. It is true that an object must define one or more fields.
Actually, there is a lot of processing that needs to be done when push a GraphQL schema. We don’t want to allow replication of fields inside the type as said by Pawan so the Parser needs to be changed in a way that it should accept even empty type declaration in the initial step. Repopulation of the interface’s fields inside the implementing type is done internally and the schema is validated after that. So even if a user just defines an empty type that does not implement an interface, it is gonna result in error during the validation because it will just be empty after internal processing.