Environment details

• OS type and version: docker image python:3.9.5-slim-buster
• Python version: 3.9.5
• pip version: 21.1.2
• google-cloud-bigquery version: 2.32.0
• opentelemetry-sdk verision: 1.9.1

Steps to reproduce

1. Setup any load job with opentelemetry enabled
2. See warning about passing None as span attribute

Stack trace

(opentelemetry.attributes) WARNING: Invalid type NoneType for attribute value. Expected one of ['bool', 'str', 'bytes', 'int', 'float'] or a sequence of those types

In _set_job_attributes() function (https://github.com/googleapis/python-bigquery/blob/main/google/cloud/bigquery/opentelemetry_tracing.py#L113) you are passing parent_job_id argument which might be None. None is invalid attribute type for opentelemetry: https://github.com/open-telemetry/opentelemetry-python/blob/45a2b350e54da9f99a718148d257ee4e28b1d8e4/opentelemetry-api/src/opentelemetry/attributes/__init__.py#L69-L79