Sharepoint numeric field set to blank

Hi

I have a sharepoint list that now has approx 20,000 rows

A few months back I added a numeric field/column after the original creation and population of the list, when the number of rows was approx 15,000

When I added the numeric column I set a default value of 0.

When I added rows from this point in time forward the new entries appeared with this column's default value of zero. 

However, for all the rows already in place, the column value appeared to default to null/blank.

I want to write an ODATA query to give me the row ID numbers for these rows which have a null/blank value. 

Any attempt to write an ODATA query with an <column name> eq null does not return anything. Equally, writing a view over the list and specifying a filter on the column name which is equal to null returns an error that the list threshold of 5000 rows is exceeded (as expected) 

I do not have the time or luxury of repopulating the list 

Any ideas as to how to either identify these rows with the blank/null value and returning their IDs (I can then write a Power automate flow to set them to zero) or, more simply, get the value to default to zero?