c# - Error -> Object reference not set to an instance of an object.

SP :
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DELIMITER $$
 
DROP PROCEDURE IF EXISTS `demo`.`sp_LoginCheck`$$
 
create PROCEDURE `demo`.`sp_LoginCheck`( 
 IN UserName1 varchar(50),
 IN Password1 varchar(50),
 OUT DoesExist int)   
    BEGIN
 declare userCount INT default 0;
 SET DoesExist = 0; -- set to false initially, we'll assume for now it doesn't exist
 SELECT COUNT(Uid) INTO userCount
 FROM tbl_Users
 WHERE username = username1 and password=password1;
 IF userCount > 0 THEN
  SET DoesExist = 1;  -- more then one returned, return true
 END IF;
    END$$
 
DELIMITER ;
 
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C# :
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  public static int CheckLogin_Instructor(string UserName, string Password)
        {
            int doesExist = 0;
            try
            {
                MySqlConnection myConn = new MySqlConnection(ConfigurationSettings.AppSettings["Con"]);
                MySqlCommand cmd = new MySqlCommand("sp_LoginCheck", myConn);
                cmd.CommandType = CommandType.StoredProcedure;
                MySqlParameter param = new MySqlParameter();
                param = cmd.Parameters.Add("@UserName1", MySqlDbType.VarChar, 50);
                param.Value = UserName;
                param = cmd.Parameters.Add("@Password1", MySqlDbType.VarChar, 50);
                param.Value = Password;
                param = cmd.Parameters.Add("@DoesExist", MySqlDbType.Int32);
                param.Direction = ParameterDirection.Output;
                myConn.Open();
                doesExist = (int)cmd.ExecuteScalar();
                myConn.Close();
            }
            catch (Exception ex)
            {
                ExceptionHandler.writeToLogFile(ex.StackTrace.ToString());
            }
            return doesExist;
        }
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