Default the error message of KustoServiceError if one is not provided.

[blalockma]

There are two locations that the exception KustoApiError is being raised in the base client:

• azure-kusto-python/azure-kusto-data/azure/kusto/data/client_base.py

  Line 124 in dc3d28b

  raise KustoApiError(response_json, message, response) from exception

• azure-kusto-python/azure-kusto-data/azure/kusto/data/client_base.py

  Line 129 in dc3d28b

  raise KustoApiError(response_json, http_response=response) from exception

The second case does not pass in a message param leading it to be an optional field. This is likely supposed to be handled by the OneApiError parsing here:

azure-kusto-python/azure-kusto-data/azure/kusto/data/exceptions.py

Line 124 in dc3d28b

self.error = OneApiError.from_dict(error_dict["error"])

but the description field there is also optional:

azure-kusto-python/azure-kusto-data/azure/kusto/data/exceptions.py

Line 71 in dc3d28b

description: Optional[str] = None

This change contains:

• Update the types of the function to be Optional so that the error is more obvious at dev-time.
• Handling the situation of a None message by defaulting it to "Unknown Kusto service error"
• Unit test to check the case shouldn't be failing anymore.