how to insert null value in a table using SQLParameter class

i am working on a windows application made in C# dotnet 2005.
in this i have a form which have a  list which gets filled from another table.
basically i have a column in a table which is forgein key.

now i wrote a update query and i want to insert null if user does not select any item from the list.
and this column is of int type in the database.

and i am using SQLParameter class to add values in update query.

here is a sample code of how i am using SQLParameter class

                SqlParameter SqlParam_GeneralLedgerAccountOID = new SqlParameter();
                SqlParam_GeneralLedgerAccountOID.ParameterName = "@OID";
                SqlParam_GeneralLedgerAccountOID.Value = OID;
                command.Parameters.Add(SqlParam_GeneralLedgerAccountOID);

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