Fixed: Backend Updates from Sonarr

Co-Authored-By: Mark McDowall <markus101@users.noreply.github.com>
Co-Authored-By: taloth <taloth@users.noreply.github.com>

src/NzbDrone.Core/Download/DownloadClientBase.cs

@@ -151,6 +151,10 @@ namespace NzbDrone.Core.Download
 
             return null;
         }
-        
+
+        public virtual void MarkItemAsImported(DownloadClientItem downloadClientItem)
+        {
+            throw new NotSupportedException(this.Name + " does not support marking items as imported");
+        }
     }
 }