Cannot process direct call with empty payload

[Cavaler]

In Azure portal, when issuing a Direct Call to a module, Payload is described as:
"Optional data to pass to the method. May be a single value or a JSON object/array."
Since it is optional, I assume it may be missing / empty.

However, issuing such a call to module using Python SDK, results in an exception before control reaches module code:

WARNING - <azure.iot.device.iothub.pipeline.pipeline_stages_iothub_mqtt.IoTHubMQTTTranslationStage object at 0x7fa98fe6b220>: Unexpected error in ._handle_pipeline_event() call: Expecting value: line 1 column 1 (char 0)

Using Azure Python SDK 2.12, with python 3.8.