I created a table in Google Data Studio using Google Sheets as the Data Set:
I changed the granularity of the date column to "Year month" to group the data in months. As you can see July 2020 is missing from the table. My source data doesn't have any values matching a date in July and that's why it is missing. But I want July 2020 to show up in the table with a "null" or "0" or "no data". I chose the setting the for "missing data" show "null" and yet its not showing up.
Added data set: Google sheet dataset