check if airdrag node exists, oterwise return null (uses standard values)

VectoCore/VectoCore/InputData/FileIO/XML/Declaration/XMLDeclarationAirdragDataProvider.cs

@@ -55,7 +55,7 @@ namespace TUGraz.VectoCore.InputData.FileIO.XML.Declaration
 
 		public SquareMeter AirDragArea
 		{
-			get { return GetDoubleElementValue(XMLNames.AirDrag_DeclaredCdxA).SI<SquareMeter>(); }
+			get { return ElementExists(XMLNames.AirDrag_DeclaredCdxA) ? GetDoubleElementValue(XMLNames.AirDrag_DeclaredCdxA).SI<SquareMeter>() : null; }
 		}
 	}
 }
\ No newline at end of file

VectoCore/VectoCore/Utils/VectoCSVFile.cs

@@ -35,10 +35,8 @@ using System.Data;
 using System.Globalization;
 using System.IO;
 using System.Linq;
-using System.Reflection;
 using System.Text;
 using System.Text.RegularExpressions;
-using DocumentFormat.OpenXml.Spreadsheet;
 using TUGraz.VectoCommon.Exceptions;
 using TUGraz.VectoCommon.InputData;
 using TUGraz.VectoCommon.Models;