Prevent select box choices filtered improperly when no query applied

Refs GH-172

keg_elements/forms/__init__.py

@@ -409,7 +409,7 @@ def filter_query(self, query):
         # Having an existing value should filter the query.
         if self.data is not None:
             data_filter = self.get_data_filter()
-            if data_filter is not None:
+            if data_filter is not None and filter_terms:
                 filter_terms.append(data_filter)
 
         # Apply filter terms with or_, or directly, depending on length.

keg_elements/tests/test_forms/test_form.py

@@ -1123,6 +1123,14 @@ def test_choices_included(self):
                                        obj=related_thing)
         assert form.thing_id.choice_values == ['', thing2.id, thing1.id]
 
+    def test_choices_data_filter_not_applied_incorrectly(self):
+        thing1 = ents.Thing.testing_create(name='foo', color='blue')
+        thing2 = ents.Thing.testing_create(name='bar', color='red')
+        thing3 = ents.Thing.testing_create(name='baz', color='purple')
+        related_thing = ents.RelatedThing.testing_create(thing=thing1)
+        form = self.create_custom_form({'query_filter': None}, obj=related_thing)
+        assert form.thing_id.choice_values == ['', thing2.id, thing3.id, thing1.id]
+
 
 class TestCollectionRelationship(RelationshipMixin):
     """Test field that corresponds to a SA collection."""