update try catch on Ampt class

csharp/Lib/Devices/AMPT/AmptDevices.cs

@@ -31,9 +31,11 @@ public class AmptDevices
         {
             return TryRead();
         }
-        catch (Exception e)
+        catch ( Exception e)
         {
+            if( e is not NullChannelException)
                 Console.WriteLine("Failed to read Ampt data \n" + e.Message);
+
             return null;
         }
     }