Programmatically Insert Null value in External Content Type

Hi There

I have programmatically create BCS and I have used Linq to sql dbml file to create get and set method.

In BCS entity i am using Linq queries which has datacontext of above linq to sql dbml file.

Everything is working fine

But when it comes to date-time column i am not able to enter null in date-time column

Eventhough that column is null sql database and also make sure null in linq to sql file

I have error message I am posting below

Details: Failed trying to write value 'null' with Type '<unavailable>' as a Field of Type 'System.DateTime'

Please some one can help please

Thank You