Duo Api failed randomly to fetch admin logs

Duo API randomly failed because of this error:

```

dumping logs
dumped successfully.
Retrieved admin Logs.
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/opt/sumologic-duo-security/lambda_function.py", line 102, in lambda_handler
logs_admin = format_admin_logs(logs_admin)
File "/opt/sumologic-duo-security/lambda_function.py", line 65, in format_admin_logs
for ph in (i['description']['phones']):
TypeError: 'NoneType' object is not iterable

```

it seems there is a bug in the code