Hi @rsanford,
Could you please share a full screenshot of the configuration of your flow?
You could add a Condition to check if the value is null, if the value is null, set the variable to 0,if no, set the variable with the value.
I have made a test on my side to create the flow as below:

I have save the question 1 answer in the Compose, and check if the compose is null.
The expression in the Condition as below:
@empty(outputs('Compose'))
When a response is submited,and the question is no answer, the flow would run successfully as below:

Please let me know if your problem could be solved.
Best regards,
Alice