gnutls_protocol_get_name() and session resumption

GnuTLS 3.6.7

On resuming a TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256 session
I'm getting a reported ciphersuite TLS1.3:NULL:256

The "NULL" derives from gnutls_cipher_suite_get_name() and
the difference from the original is that the kx has changed
from 12 (GNUTLS_KX_ECDHE_RSA) to 14 (GNUTLS_KX_ECDHE_PSK).


Should I be using gnutls_kx_get_name() (&c for cipher and mac)
separately, rather than gnutls_cipher_suite_get_name() ?
-- 
Thanks,
  Jeremy