Pass NULL instead of default in SQL parameter while passing from C#

Hi Experts,
I am calling store procedure from ASP.Net.
The call I am getting using profiler is : EXEC usp_Update @Id=204,@Order=1,@IsDependent=default. I want to pass NULL instead of default.
The call should be EXEC usp_Update @Id=204,@Order=1,@IsDependent=NULL.

"EXE usp_CoveragesUpdate @Id, @Order, @IsDependent" new SqlParameter("@Id",lstcovarage.ID), new SqlParameter("@Order", lstcovarage.Order), new SqlParameter("@IsDependent", lstcovarage.IsDependent)

Also If I use 
new SqlParameter("@Id",SqlDbType.Int,lstcovarage.ID) Since my Id is nullable 
public int? Id { get; set; } It throws an error "cannot convert int? to int"
...