VS2005 has a double.TryParse

If the TryParse failes, then set the value to DBNull.Value
while (dr.Read())
//dr is an instance of sqlDataReader
{
   double minAirTemp = (double)(Single)dr["minAirTemp"];
   // minAirTemp is column in SQLExpress table  (data type: real, allows
nulls)
}

The above code works. But when there are NULL, I get the following error
System.InvalidCastException: Specified cast is not valid

To solve this problem, I spent a day on Google. Finally I got a hint from
http://www.codeproject.com/cs/database/SmartReader.asp and replaced the code
line in while{} as follows:

double minAirTemp1 = (dr.IsDBNull(dr.GetOrdinal("minAirTemp1")))
? 9999 : double.Parse(dr["minAirTemp1"].ToString()); //9999 to respresent
nulls
This works for me for now. But just wondering, whether there is a better
method to deal with such a situation????
Can someone be kind to point me to some suitable reference !
Thanks !

I have a big class called SqlHelper full of methods like:

public static decimal GetReaderDecimal(IDataRecord dr, int column,
decimal ifNull)
{
  return dr.IsDBNull(column)? ifNull : dr.GetDecimal(column);
}