AutoCAD P&ID

[#1]

I'm have problems casting a PnPRow column object to type double. I get a "Specified cast is not valid." error message thrown. However, I have no problems casting a PnPRow to type long (for PnPID) or string (for String data types in P&ID Class Definitions). Could the casting error be due to the value being empty? I do a check for (row[c] == null) but it is never null. Here are examples that work:

PnPRow row;
//After obtaining PnPRow...
int pnpid = (int)row[0]; //PnPID column, works fine
string tempstr = (string)row[c];
double num = (double)row[c]; //Error!

 As background, here is the full code for anybody on here to test and hopefully answer my question:

PlantProject proj = PlantApplication.CurrentProject;
ProjectPartCollection projParts = proj.ProjectParts;
PnIdProject pnidProj = (PnIdProject)projParts["PnId"];
DataLinksManager dlm = pnidProj.DataLinksManager;
PnPDatabase db = dlm.GetPnPDatabase();
PnPTables pnpTbls = db.Tables;
PnPTable aTbl = pnpTbls["Instrumentation"];

PnPColumns cols = aTbl.AllColumns;
List<DataType> dataTypes = new List<DataType>(50);
List<string> colNames = new List<string>(50);
List<int> colNums = new List<int>(50);
string cmdVals, cmdFlds, tempstr, typestr;
string cmdText = "CREATE TABLE [INSTRUMENT LIST] (";

int j = 0;
foreach (PnPColumn col in cols)
{
	tempstr = col.Name.Replace(' ', '_') + '_'; //Replace spaces with '_' and append '_' to make field names unique
	typestr = col.ColumnType.Name;
	switch (typestr[0])
	{
		case 'I':
			cmdText += tempstr + " LONG,";
			dataTypes.Add(DataType.Long);
			break;
		case 'D':
			if (typestr[1] == 'a')
			{
				cmdText += tempstr + " DATETIME,";
				dataTypes.Add(DataType.Date);
			}
			else
			{
				cmdText += tempstr + " DOUBLE,";
				dataTypes.Add(DataType.Double);
			}
			break;
		case 'S':
			cmdText += tempstr + " CHAR(255),";
			dataTypes.Add(DataType.String);
			break;
		default:
			txtFeedback.Text += "Unknown data type '" + typestr + "' found with column " + col.Name + "; defaulting to string.";
			cmdText += tempstr + " CHAR(255),";
			dataTypes.Add(DataType.String);
		break;
	}
	cmdFlds += tempstr + ',';
	colNames.Add(tempstr);
	colNums.Add(j);
	cmdVals += '@' + tempstr + ',';
	j++;
}
cmdVals = cmdVals.Substring(0, cmdVals.Length - 1);
cmdFlds = cmdFlds.Substring(0, cmdFlds.Length - 1);

string xlFile = "C:\\temp\\output.xlsx";
if (File.Exists(xlFile))
	File.Delete(xlFile);
if (File.Exists("C:\\temp\\blank.xlsx"))
	File.Copy("C:\\temp\\blank.xlsx", xlFile);
using (OleDbConnection xlCon = new OleDbConnection("Provider = Microsoft.ACE.OLEDB.12.0; " +
				"Data Source = " + xlFile + ";Mode=ReadWrite;" +
				"Extended Properties='Excel 12.0;HDR=YES;'"))
{
	xlCon.Open();
	OleDbCommand xlCmd = new OleDbCommand(cmdText.Substring(0, cmdText.Length - 1) + ')', xlCon);
	xlCmd.ExecuteNonQuery(); //Create [INSTRUMENT LIST] table
	xlCmd = null;

	PnPRow[] rows = aTbl.Select();
	foreach (PnPRow row in rows)
	{
		xlCmd = new OleDbCommand("INSERT INTO [INSTRUMENT LIST](" + cmdFlds + ") values(" + cmdVals + ')', xlCon);
		j = 0;
		foreach(int c in colNums)
		{
			if (row[c] == null)
				xlCmd.Parameters.AddWithValue("@" + colNames[j], DBNull.Value);
			else
			{
				switch (dataTypes[j])
				{
					case DataType.Date:
						DataType tempDT = (DateTime)row[c];
						xlCmd.Parameters.AddWithValue("@" + colNames[j], tempDT);
						break;
					case DataType.Double:
						double tempDbl = (double)row[c];	// ***THIS CRASHES***
						xlCmd.Parameters.AddWithValue("@" + colNames[j], tempDbl);
						break;
					case DataType.Long:
						tempLong = (long)row[c];
						xlCmd.Parameters.AddWithValue("@" + colNames[j], tempLong);
						break;
					//case DataType.General:
					//case DataType.String:
					default:
						tempstr = row[c].ToString();
						if (tempstr.Length > 0)
							xlCmd.Parameters.AddWithValue("@" + colNames[j], tempstr);
						else
							xlCmd.Parameters.AddWithValue("@" + colNames[j], DBNull.Value);
						break;
				}
			}
			j++;
		}
		xlCmd.ExecuteNonQuery();	//Insert a row of data into the [INSTRUMENT LIST] table
	}
	xlCon.Close();
}

Is it failing because the double value is empty? If so, how would I check for an empty value before assigning to [double num]?

Thanks in advance.