IsNull (geometry Data Type)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
The type of a geometry instance is null. Returns 0 if the instance isn't null.
Syntax
.IsNull
Return Types
SQL Server type: bit
CLR type: SqlBoolean
Remarks
IsNull can be used to test whether a geometry instance is null. IsNull returns 0 if the instance isn't null, but null if the instance is null.
This method is primarily used by the SQL Server infrastructure; it isn't recommended that you use IsNull to test whether an instance is null.