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