message: Validate that ECIES private keys are not empty.
  Not sure what else that we can validate here.
  GitOrigin-RevId:
diff: @@ -140,7 +140,9 @@ class EciesAeadHkdfPrivateKeyManager
  @Override
  protected void validateKey(EciesAeadHkdfPrivateKey keyProto) throws GeneralSecurityException {
  - // TODO(b/74249437): add more checks.
  + if (keyProto.getKeyValue().isEmpty()) {
  + throw new GeneralSecurityException("invalid ECIES private key");
  + }
  Validators.validateVersion(keyProto.getVersion(), VERSION);
  HybridUtil.validate(keyProto.getPublicKey().getParams());
  }
  