Working with C# dictionary

Check dictionary value if it's empty

dictionary.ElementAt(i).Value == DBNull.Value

Check string value 

if (String.IsNullOrWhiteSpace(mystring))

equals to..

if (mystring == null || mystring == String.Empty || mystring.Trim().Length == 0) 

earlier version

if (String.IsNullOrEmpty(mystring) || mystring.Trim().Length == 0)

equals to..

if (mystring== null || mystring== String.Empty)