c#中数据库调用抛出意外错误

我已经编写了以下方法来从数据库中获取对象列表:

public IEnumerable<ProductDBKey6> AssignProductKey6 (string strProdList)
        {
            List<ProductDBKey6> lstProdDBKey6 = new List<ProductDBKey6>();
            // Create the parameters collection
            var parameters = new Collection<SqlParameter>();
            // Add each parameter.  Entity will not work without all params in the correct order            
            SqlParameter param = StoredProcedureParameterBuilder.StringParam("@ProductID", strProdList, -1);
            int? tempTimeout = this.Database.CommandTimeout;
            this.Database.CommandTimeout = 300;
            lstProdDBKey6 = this.Database.SqlQuery<ProductDBKey6>("spc.FindProductDBKeyForID", param).ToList();
            this.Database.CommandTimeout = tempTimeout;
            return lstProdDBKey6;
        }

但是我收到了@ProductID参数没有提供的错误。以下是StoredProcedureParameterBuilder类中编写的代码:

internal static class StoredProcedureParameterBuilder
    {
        internal static SqlParameter StringParam(string paramName, string paramValue, int paramSize)
        {
            SqlParameter outParam = new SqlParameter
            {
                ParameterName = paramName,
                SqlDbType = System.Data.SqlDbType.VarChar,
                Direction = System.Data.ParameterDirection.Input,
                Size = paramSize
            };
            if (string.IsNullOrEmpty(paramValue))
            {
                outParam.Value = DBNull.Value;
            }
            else
            {
                outParam.Value = paramValue;
            }
            return outParam;
        }
    }

存储过程只接受一个参数@ProductID。下面是存储过程声明:

ALTER PROCEDURE [spc].[FindProductDBKeyForID] (
        @ProductID          VARCHAR(MAX)
)

请帮忙解决这个错误

lstProdDBKey6 =
      this
      .Database.SqlQuery<ProductDBKey6>("spc.FindProductDBKeyForID", param)
      .ToList();

lstProdDBKey6 =
      this
      .Database.SqlQuery<ProductDBKey6>("exec spc.FindProductDBKeyForID @ProductID", param)
      .ToList();