diff --git a/apps/collection/models.py b/apps/collection/models.py
index 14bd99c0..d9256743 100644
--- a/apps/collection/models.py
+++ b/apps/collection/models.py
@@ -24,7 +24,8 @@ class CollectionNameMixin(models.Model):
 
 class CollectionDateMixin(models.Model):
     """CollectionDate mixin"""
-    start = models.DateTimeField(_('start'))
+    start = models.DateTimeField(blank=True, null=True, default=None,
+                                 verbose_name=_('start'))
     end = models.DateTimeField(blank=True, null=True, default=None,
                                verbose_name=_('end'))
 
@@ -110,20 +111,29 @@ class Collection(ProjectBaseMixin, CollectionDateMixin,
     @property
     def related_object_names(self) -> list:
         """Return related object names."""
-        raw_object_names = []
-        for related_object in [related_object.name for related_object in self._related_objects]:
-            instances = getattr(self, f'{related_object}')
+        raw_object_names = {}
+        for related_object in [(related_object.id, related_object.name) for related_object in self._related_objects]:
+            instances = getattr(self, f'{related_object[1]}')
             if instances.exists():
                 for instance in instances.all():
-                    raw_object_names.append(instance.slug if hasattr(instance, 'slug') else None)
+                    raw_object_names[related_object[0]] = instance.slug if hasattr(instance, 'slug') else None
 
         # parse slugs
-        object_names = []
+        related_objects = []
+        object_names = set()
         re_pattern = r'[\w]+'
-        for raw_name in raw_object_names:
-            result = re.findall(re_pattern, raw_name)
-            if result: object_names.append(' '.join(result).capitalize())
-        return set(object_names)
+        for object_id in raw_object_names:
+            result = re.findall(re_pattern, raw_object_names[object_id])
+            if result:
+                name = ' '.join(result).capitalize()
+                if name not in object_names:
+                    related_objects.append({
+                        'id': object_id,
+                        'name': name
+                    })
+                object_names.add(name)
+
+        return related_objects
 
 
 class GuideTypeQuerySet(models.QuerySet):