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/account/forms.py

@@ -57,10 +57,9 @@ class NoOffsetNominalAccount:
     """The validator to check nominal account is not to be offset."""
 
     def __call__(self, form: FlaskForm, field: BooleanField) -> None:
+        assert isinstance(form, AccountForm)
         if not field.data:
             return
-        if not isinstance(form, AccountForm):
-            return
         if form.base_code.data is None:
             return
         if form.base_code.data[0] not in {"1", "2"}: