Searching For Records With Null Values

I'm hoping someone can help me with my problem.

I'm reading in records from a 'flat file' and loading them into sql.

I have 5 values I'm loading in.  I first check my sql db, if all 5 values match a current record in sql, I don't want to load the record, because it's already there.  If it doesn't exist, I need to load it.

It works fine as long as none of my values are NULL.  But if I have a record with a field, say Gender, that is null, if its a new record it loads fine, setting gender to NULL in sql.  But then when I encounter another record, which is identical, I'm testing to see if it already exists by  doing a 'select where Gender = @Gender'   and it always returns that the record does not exist in the db - even though it exists (because its using the = instead of is null)! 

I need some mechanism where if the value is null it tests 'Gender is null'  but if there is a value, it tests gender=gender, [and I need this for all my parameters].  Or is there some other way to do this? 

 

 Here is my code for looking to see if the record exists:  

public static int ExistInsured(int CaseID, object InsuredLastName, object DateOfBirth, object CurrentAge, object Gender)

{SqlConnection conn = new SqlConnection(connStng.ToString());

SqlCommand cmd = new SqlCommand("SELECT top 1 InsuredID from Insured Where PolicyID = (Select PolicyID from Policy where CaseID = @CaseID) and LastName = @InsuredLastName and DateofBirth = @DateofBirth and Gender = @Gender", conn);

 int result = -1;

cmd.CommandType = CommandType.Text;cmd.Parameters.AddWithValue("@CaseID", CaseID);

cmd.Parameters.AddWithValue("@InsuredLastName", InsuredLastName);cmd.Parameters.AddWithValue("@DateOfBirth", DateOfBirth);

cmd.Parameters.AddWithValue("@CurrentAge", CurrentAge);

cmd.Parameters.AddWithValue("@Gender", Gender);

 

 

conn.Open();

try

{object ret = cmd.ExecuteScalar();

if ((ret != null) && (ret is int))result = (int)ret;

}

finally

{

conn.Close();

}return result;

 

}