@semanticNonNull

directive @semanticNonNull(levels: [Int!]! = [0]) on FIELD_DEFINITION

type User {
    # email is semantically non-null and can be generated as non-null by error-handling clients.
    email: String @semanticNonNull
}

type User {
    # friends is semantically non null
    friends: [User] @semanticNonNull # same as @semanticNonNull(levels: [0])
    
    # every friends[k] is semantically non null
    friends: [User] @semanticNonNull(levels: [1])
    
    # friends as well as every friends[k] is semantically non null
    friends: [User] @semanticNonNull(levels: [0, 1])
}