def METHOD_NAME(self):
    payload_json = """{"appconnectPrivateKey": ""}"""
    payload = json.loads(payload_json)
    serializer = AppStoreUpdateCredentialsSerializer(data=payload)
    assert not serializer.is_valid()
    # There's no meaning to setting this to empty string, the entire set of
    # credentials should be deleted instead of this
    assert serializer.errors["appconnectPrivateKey"][0].code == "blank"