One column in my database (of type double) has some null values. I am executing a sored procedure to get the data in my app

 wipDBTableAdapters.XLSFacturiTableAdapter TAFacturi = new wipDBTableAdapters.XLSFacturiTableAdapter();
               var dtfacturi = TAFacturi.GetData(CodProiect);

Then i try to do something like this:

if (dtfacturi[i].CANTITATE == null)
   {
    //do something
   }

this is giving a warning :

The result of the expression is always 'false' since a value of type 'double' is never equal to 'null' of type 'double?

However when i run my code i get the following exception:

StrongTypingException
The value for column 'CANTITATE' in table 'XLSFacturi' is DBNull. 

How am I supposed to resolve this ?