bugfix and making more robust

core/forms.py

@@ -208,7 +208,9 @@ class EntranceLetterForm(ModelForm):
     Nb. The relationship between caves and entrances has historically been a many to many relationship.
     With entrances gaining new caves and letters when caves are joined.
     """
-    entranceletter = forms.CharField(required=False, widget=forms.TextInput(attrs={"size": "2"}))
+    
+    # This only needs to be required=True for the second and subsequent entrances, not the first. Tricky.
+    entranceletter = forms.CharField(required=True, widget=forms.TextInput(attrs={"size": "2"}))
 
     class Meta:
         model = CaveAndEntrance