Raise error when dora python operator doesn't return dora status

[Felixhuangsiling]

Sometimes I forgot to put operators DoraStatus.CONTINUE which will fail the code without let me knowing it.

Expected behavior
I would like to have a error being raised to let me know that my code failed.

Environments (please complete the following information):

• System info: linux
• Dora version: 0.2.6
• Python version: 3.8.10

[haixuanTao]

It seems that i cannot reproduce this error.

I get the following error:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
RuntimeError: Dora Runtime raised an error.

Caused by:
   0: main task failed
   1: operator object_detection/op raised an error
   2: error in Python module at /home/peter/Documents/work/dora/examples/python-operator-dataflow/object_detection.py
   3: on_event must have enum return value
   4: AttributeError: 'NoneType' object has no attribute 'value'