Merge branch 'matej-drobna-vylepseni'

seminar/admin.py

@@ -495,6 +495,8 @@ class ProblemZadanyAdmin(ProblemAdmin):
     ]
 
     def cislo_zadani_link(self, obj):
+        if not obj.cislo_zadani:
+            return ""
         return mark_safe('<a href="{}">{}</a>'.format(
             reverse("admin:seminar_cislo_change", args=(obj.cislo_zadani.pk,)),
             obj.cislo_zadani
@@ -505,6 +507,8 @@ class ProblemZadanyAdmin(ProblemAdmin):
     # nějak zjednodušit, např. tímto?
     # https://github.com/gitaarik/django-admin-relation-links
     def cislo_reseni_link(self, obj):
+        if not obj.cislo_reseni:
+            return ""
         return mark_safe('<a href="{}">{}</a>'.format(
             reverse("admin:seminar_cislo_change", args=(obj.cislo_reseni.pk,)),
             obj.cislo_reseni