Fix bugu u exportu: end-year = 'None'

seminar/models.py

@@ -195,7 +195,7 @@ class Resitel(SeminarModelBase):
                 'gender': 'M' if self.pohlavi_muz else 'F',
                 'born': self.datum_narozeni.isoformat() if self.datum_narozeni else '',
                 'email': self.email,
-                'end-year': self.rok_maturity,
+                'end-year': self.rok_maturity or '',
 
                 # TODO(gavento): Adresa skoly, kdyz preferuje zasilani tam?
                 'street': self.ulice,