Don't process internal models twice if imported from project

src/dipdup/database.py

@@ -394,8 +394,15 @@ def prepare_models(package: str | None) -> None:
     EXECUTOR_CACHE.clear()
 
     db_tables: set[str] = set()
+    qualnames: set[str] = set()
 
     for app, model in iter_models(package):
+        # NOTE: Don't process internal models twice if imported from project
+        qualname = f'{model.__module__}.{model.__qualname__}'
+        if qualname in qualnames:
+            continue
+        qualnames.add(qualname)
+
         # NOTE: Enforce our class for user models
         if app != 'int_models' and not issubclass(model, dipdup.models.Model):
             raise InvalidModelsError(

src/dipdup/fields.py

@@ -130,9 +130,7 @@ def __init__(self, max_digits: int, decimal_places: int, **kwargs: Any) -> None:
         self.quant = Decimal('1' if decimal_places == 0 else f'1.{("0" * decimal_places)}')
 
     def to_python_value(self, value: Any) -> Decimal | None:
-        if value is None:
-            value = None
-        else:
+        if value is not None:
             value = Decimal(value).quantize(self.quant).normalize()
         self.validate(value)
         return value  # type: ignore[no-any-return]