Add new Series and choose it from combobox

[Katarzyna-Kadziolka]

Repro steps:

1. Add new Book
2. Add new Series
3. Choose new series from Combobox
4. Click Add Book

Expected result: Book is added
Actual result: Error occurs

[Morasiu]

Possibly to fix this, you should detach Series entity, after you add it (after SaveChanges).