SqlCommand.ExecuteReader使用带输出参数的存储过程不返回任何行

我有一个接受输入并返回多列的存储过程。当我从SSMS和VS 2013内部执行存储过程时，该存储过程可以工作。但是，当我尝试使用SqlCommand.ExecuteReader执行该存储过程时，阅读器中没有任何行。如果我从proc和SqlCommand中删除输出参数，同时仍保留一个输入参数，则可以返回要查找的行。

这是存储的过程

create Proc sp_ReturnSingleGame
    @GameName varchar(100) output,
    @PlatformName varchar(50) output,
    @ConditionShortDescription varchar(30) output,
    @RetailCost decimal(6,2) output,
    @InStock bit output,
    @GameID int
AS
    select @GameName = GameName, @PlatformName = PlatformName, 
           @ConditionShortDescription = ConditionShortDescription, @RetailCost = RetailCost
         from   Games inner join Condition 
         on     Games.ConditionID = Condition.ConditionID 
                inner join ConsolePlatform
         on Games.PlatformID = ConsolePlatform.PlatformID
         Where Games.GameID = @GameID

    if exists (select GameID 
               From SaleItemized
               Where GameID = @GameID)
        Begin
            set @InStock = 1;
        end
    else
        Begin
            set @InStock = 0;
        end

这是我的C＃代码

public Game ReturnSingleGame(int gameId)
{
    SqlConnection connection = new SqlConnection(@"server=mylaptop; integrated security=true; database=GameStoreDB;");

    SqlCommand command = this.ReturnCommandForSp_ReturnSingleGame(connection, gameId);

    try
    {
        connection.Open();
        SqlDataReader reader = command.ExecuteReader();
        if (reader.HasRows == true)
        {
            reader.Read();
            game.GameId = gameId;
            game.GameName = reader["GameName"].ToString();
            game.PlatformName = reader["PlatformName"].ToString();
            game.RetailCost = (decimal) reader["RetailCost"];
        }
        else
        {
            var exception = new ApplicationException("Game was not found");
            throw exception;
        }
    }
    catch (Exception)
    {
        throw;
    }
    finally
    {
        connection.Close();
    }
    return game;
}

private SqlCommand CommandForSp_ReturnSingleGame(SqlConnection connection, int gameId)
{
    string storedProc = @"dbo.sp_ReturnSingleGame";

    SqlCommand command = new SqlCommand(storedProc, connection);
    command.CommandType = CommandType.StoredProcedure;

    command.Parameters.Add("@GameName", SqlDbType.VarChar, 100, "GameName");
    command.Parameters["@GameName"].Direction = ParameterDirection.Output;

    command.Parameters.Add("@PlatformName", SqlDbType.VarChar, 50, "PlatformName");
    command.Parameters["@PlatformName"].Direction = ParameterDirection.Output;

    command.Parameters.Add("@ConditionShortDescription", SqlDbType.VarChar, 30, "ConditionShortDescription");
    command.Parameters["@ConditionShortDescription"].Direction = ParameterDirection.Output;

    command.Parameters.Add("@RetailCost", SqlDbType.Decimal);
    command.Parameters["@RetailCost"].SourceColumn = "RetailCost";
    command.Parameters["@RetailCost"].Precision = 6;
    command.Parameters["@RetailCost"].Scale = 2;
    command.Parameters["@RetailCost"].Direction = ParameterDirection.Output;

    command.Parameters.Add("@InStock", SqlDbType.Bit);
    command.Parameters["@InStock"].SourceColumn = "InStock";
    command.Parameters["@InStock"].Direction = ParameterDirection.Output;

    command.Parameters.Add("@GameID", SqlDbType.Int).Value = gameId;
    command.Parameters["@GameID"].SourceColumn = "GameID";
    command.Parameters["@GameID"].Direction = ParameterDirection.Input;

    command.Prepare();

    return command;
}