fix EmployeeBackSerializers

apps/establishment/serializers/back.py

@@ -186,16 +186,19 @@ class EmployeeBackSerializers(serializers.ModelSerializer):
         """Get last list actual public_mark"""
         qs = obj.establishmentemployee_set.actual().order_by('-from_date')\
             .values('establishment__public_mark').first()
-        return qs['establishment__public_mark']
+        return qs['establishment__public_mark'] if qs else None
 
 
     def get_positions(self, obj):
         """Get last list actual positions"""
         est_id = obj.establishmentemployee_set.actual().\
-            order_by('-from_date').first().establishment_id
+            order_by('-from_date').first()
+
+        if not est_id:
+            return None
 
         qs = obj.establishmentemployee_set.actual()\
-            .filter(establishment_id=est_id)\
+            .filter(establishment_id=est_id.establishment_id)\
             .prefetch_related('position').values('position')
 
         positions = models.Position.objects.filter(id__in=[q['position'] for q in qs])
@@ -205,11 +208,14 @@ class EmployeeBackSerializers(serializers.ModelSerializer):
     def get_establishment(self, obj):
         """Get last actual establishment"""
         est = obj.establishmentemployee_set.actual().order_by('-from_date')\
-            .first().establishment
+            .first()
+
+        if not est:
+            return None
 
         return {
-            "id": est.id,
-            "slug": est.slug
+            "id": est.establishment.id,
+            "slug": est.establishment.slug
         }
 
     class Meta: