OLEDBReader Porblem

Hi every body!
                I'm facing the problem in following code. In database there is an empty field when i try to read it the error came on console. the code is given following.

It show me the error that System.InvalidCastException: Specified cast is not valid. How to remove the error.....

try

{

conn.Open();

string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0;data source=Z:\\ptcl.accdb";OleDbConnection conn = new

OleDbConnection(connectionString);string sql = "SELECT * FROM 51";OleDbCommand cmd = new OleDbCommand(sql, conn);

reader = cmd.ExecuteReader();

OleDbDataReader reader;String name = null;
string name = null;
while (reader.Read())
{       
        if(reader.GetString())
        {
                Console.WriteLine("Feild Empty");
        }
}
}

catch(Exception ex)

{

Console.WriteLine(ex.ToString());

}