Null (geography Data Type)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
A read-only property providing a null instance of the geography type.
Syntax
Null
Arguments
Return Types
SQL Server type: geography
CLR type: SqlGeography
Remarks
Examples
The following example retrieves a null geography instance.
DECLARE @g geography;
SET @g = geography::[Null];
SELECT @g