What is `COLUMN_NAME_NULLABLE`

I was going through the Android Documentation of how to do database operations on Android using SqlLite. In the "Put information into database" section the insert() method takes 3 parameters

1) Table Name

2) .COLUMN_NAME_NULLABLE

3) values

The documentation below it says 'COLUMN_NAME_NULLABLE' the second argument provides the name of a column in which the framework can insert NULL in the event that the ContentValues is empty (if you instead set this to "null", then the framework will not insert a row when there are no values).

But i do not have any field in FeedEntry class with a value as 'COLUMN_NAME_NULLABLE'. I do not understand from where this is coming from.