Replaced the if checks with assert in the IsBalanced validator of the currency sub-form of the transaction form, the NoOffsetNominalAccount validator of the account form, and the CodeUnique validator of the currency form.

src/accounting/currency/forms.py

@@ -32,10 +32,9 @@ class CodeUnique:
     """The validator to check if the code is unique."""
 
     def __call__(self, form: FlaskForm, field: StringField) -> None:
+        assert isinstance(form, CurrencyForm)
         if field.data == "":
             return
-        if not isinstance(form, CurrencyForm):
-            return
         if form.obj_code is not None and form.obj_code == field.data:
             return
         if db.session.get(Currency, field.data) is not None: