IsNull (geography Data Type)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
A property that specifies if the geography instance is null. Returns 'TRUE' if the instance is null; returns 0 if the instance is not null.
Syntax
.IsNull
Return Types
SQL Server type: bit
CLR type: SqlBoolean
Remarks
IsNull can be used to test whether a geography instance is null. This can produce somewhat confusing results, returning 0 if the instance is not null, but null if the instance is null.
This method is primarily used by the SQL Server infrastructure; it is recommended that you use the T-SQL predicate IS NULL to test whether a geography instance is null. For more information on the T-SQL predicate IS NULL, see IS NULL (Transact-SQL).