Fall back when a translation is stored as an empty string

modeltrans/fields.py

@@ -1,7 +1,7 @@
 from django.core.exceptions import ImproperlyConfigured
-from django.db.models import F, JSONField, fields
+from django.db.models import F, JSONField, Value, fields
 from django.db.models.fields.json import KeyTextTransform
-from django.db.models.functions import Cast, Coalesce
+from django.db.models.functions import Cast, Coalesce, NullIf
 from django.utils.translation import gettext
 
 from .conf import get_default_language, get_fallback_chain, get_modeltrans_setting
@@ -247,6 +247,14 @@ def as_expression(self, bare_lookup, fallback=True):
         # and now, add the list of fallback languages to the lookup list
         for fallback_language in fallback_chain:
             lookups.append(self._localized_lookup(fallback_language, bare_lookup))
+
+        # An empty translation in `i18n` must be skipped, just like `__get__()` does, so
+        # `NULLIF(<lookup>, '')` is used to make `COALESCE` continue to the next language
+        # in the chain. The lookup for the default language is a plain reference to the
+        # original field (a string), which is the last resort and is left as it is.
+        lookups = [
+            lookup if isinstance(lookup, str) else NullIf(lookup, Value("")) for lookup in lookups
+        ]
         return Coalesce(*lookups, output_field=self.output_field())
 
 

tests/test_querysets.py

@@ -771,3 +771,35 @@ def test_values_kwarg_lower(self):
     def test_values_spanning_relation(self):
         qs = Blog.objects.all().order_by("title_nl").values_list("title_nl", "category__name_nl")
         self.assertEqual(list(qs), [(None, None), ("Kikker", "Amfibiën"), ("Valk", "Vogels")])
+
+
+class FallbackEmptyStringTest(TestCase):
+    """
+    An empty translation in `i18n` must be skipped while building the fallback
+    expression, just like `TranslatedVirtualField.__get__()` skips it.
+    """
+
+    def setUp(self):
+        Blog.objects.bulk_create(
+            [Blog(title="Falcon", title_nl=""), Blog(title="Frog", title_nl="Kikker")]
+        )
+
+    def test_values_i18n(self):
+        with override("nl"):
+            self.assertEqual(
+                set(Blog.objects.values_list("title_i18n", flat=True)), {"Falcon", "Kikker"}
+            )
+
+    def test_filter_i18n(self):
+        with override("nl"):
+            self.assertEqual(
+                {m.title for m in Blog.objects.filter(title_i18n="Falcon")}, {"Falcon"}
+            )
+
+    def test_values_i18n_custom_fallback(self):
+        Challenge.objects.create(default_language="nl", title="Hurray", i18n={"title_nl": ""})
+
+        with override("de"):
+            self.assertEqual(
+                set(Challenge.objects.values_list("title_i18n", flat=True)), {"Hurray"}
+            )