How can I get Zapier MySQL “update row” to update

I have created a Zapier Zap to populate data from a SmartSheet to a MySQL database. I have it branching so if the row does not already exist in MySQL a new row is created. This part works fine. In my second branch, if the row already exists then the data in the row is updated with new data from the SmartSheet row. When existing data is replaced with new data the Zap works fine. E.g. for an example existing MySQL row:

+--------+---------------+--------------------+
| row_id | email_comment | smartsheet_orig_id |
+--------+---------------+--------------------+
|    895 | easy          |  6876364645150921  |
+--------+---------------+--------------------+

In the SmartSheet if the user replaces the comment with another, the MySQL data is updated successfully, e.g:

+--------+---------------+--------------------+
| row_id | email_comment | smartsheet_orig_id |
+--------+---------------+--------------------+
|    895 |  difficult    |  6876364645150921  |
+--------+---------------+--------------------+

But, if the user has deleted the comment in SmartSheet and not replaced it with another, leaving the comment empty, the data is not removed from the corresponding MySQL record e.g:

+--------+---------------+--------------------+
| row_id | email_comment | smartsheet_orig_id |
+--------+---------------+--------------------+
|    895 |  difficult    |  6876364645150921  |
+--------+---------------+--------------------+

What I need the MySQL record to look like in this case would be:

+--------+---------------+--------------------+
| row_id | email_comment | smartsheet_orig_id |
+--------+---------------+--------------------+
|    895 |               |  6876364645150921  |
+--------+---------------+--------------------+

After quite a lot of testing, and a conversation with Zapier support it appears the problem is that Null values are removed from the Zapier Code output step. So, the above case, this is a summary of what I'm expecting to happen:

Zapier Code step: email_comment = Null --> MySQL Update Row step: email_comment = Null

But at the output of the Code step my Null value for emai_comment is stripped and so the MySQL Update Row Zap step interprets the record as not needing to be updated as there is no change and leaves the old value there.

I have tried, in my code, passing an empty string " " instead of a Null but I get the exact same result. The only way around I can see is to pass on some empirical character and then in the Update Row step replace that with a Null to store in the record but I can't see a way of doing that in Zapier.

I have searched Google and Here for others wrestling with this issue but have drawn a complete blank. The search strings I have been using are [Zapier] delete data, [Zapier] remove data and [Zapier] Null. None of the results of those searches seem to be dealing with the issue I am having.

This is the Python code I'm using to gather the inputs from SmartSheet:

#for a non existent input store an empty value
def gather_vals(inp):
    return input_data.get(inp, emptyInput)

def pull_inputs(inputs, vinputs):
    for key, value in zip(vinputs,inputs):
        v = gather_vals(value)
        d_inputs.update( {key:v})

x_vinputs = ['input_equipment', 'input_from', 'input_to', 'input_description', 'input_contractor', 'input_booked', 'input_confirmed', 'input_job_no', 'input_complete', 'input_est_val', 'input_inv_val', 'input_inv_no', 'input_book', 'input_update', 'input_comments_email']
x_inputs = ['equipment', 'from', 'to', 'description', 'contractor', 'booked', 'confirmed', 'job_no', 'complete', 'est_val', 'inv_val', 'inv_no', 'book', 'update', 'comments_email']

# Gather rest of inputs
emptyInput = None
d_inputs = {}
#gather pick-up/delivery date/time input data
pull_inputs(x_inputs, x_vinputs)
results.update(d_inputs)

return results

It appears that the code works, it returns no errors and when there is an updated actual value in SmartSheet it is updated in MySQL but when the comment is deleted the old value is left in MySQL.

I'm hoping someone may have a suggestion for me to follow.

This is the Zap flow:

Zapier support tells me the problem is that Nulls are being stripped off the output of the Python code step circled in red. The Nulls need to flow through to the Update Row step.

Manually entering NULL or Null or null in the Update Row step results in a string of characters being sent to MySQL. See the outpt from MySQL Workbench for that record: