Using Apache Superset and Google Sheets, how to check that the value is not null, as well as add other conditions? [migrated]

I'm using Apache Superset to retrieve data from Google Sheets. Shillelagh is used for integration with Google Sheets.

I have a column which specifies a deadline for tasks. If the task doesn't have a deadline, the field is empty.

The problem occurs, when I try to filter dates by this column.The query looks something like this:

SELECT *FROM"https://docs.google.com/spreadsheets/d/****"WHERE Deadline is not NULL AND Deadline < date('2021-12-31')

If I write each part of the query separately, it works:

• WHERE Deadline is not NULL --> Returns rows 1 & 2
• WHERE Deadline < date('2021-12-31') --> Returns row 2 & 3

The problem occurs when I try to use both of these conditions, so I would only get the tasks that have deadline specified & the deadline was missed (row 2):

• WHERE Deadline is not NULL AND Deadline < date('now') --> This returns gsheets error: No valid filter found

I made sure that the data in the spreadsheet is date or null. Superset recognizes the column as a DATETIME type.

I'm at a loss why this is not working when combined. Any help is appreciated.