fix: filter None values from OpenTelemetry attributes (#1567)

* fix: filter None values from OpenTelemetry attributes

* moved filtering out before return value

Author: galz10

google/cloud/bigquery/opentelemetry_tracing.py

@@ -97,6 +97,11 @@ def _get_final_span_attributes(attributes=None, client=None, job_ref=None):
         final_attributes.update(job_attributes)
     if attributes:
         final_attributes.update(attributes)
+
+    filtered = {k: v for k, v in final_attributes.items() if v is not None}
+    final_attributes.clear()
+    final_attributes.update(filtered)
+
     return final_attributes