do not require related document

sdbs_pile/pile/migrations/0012_auto_20200610_1013.py

@@ -0,0 +1,18 @@
+# Generated by Django 3.0.4 on 2020-06-10 08:13
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('pile', '0011_document_related'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='document',
+            name='related',
+            field=models.ManyToManyField(blank=True, related_name='_document_related_+', to='pile.Document'),
+        ),
+    ]

sdbs_pile/pile/models.py

@@ -57,7 +57,7 @@ class Document(SoftDeletableModel):
                               max_length=3, choices=DocumentStatus.choices, default=DocumentStatus.STANDARD)
     tags = models.ManyToManyField(Tag, related_name="documents", blank=True)
     uploaded = models.DateTimeField(auto_now_add=True, null=True)
-    related = models.ManyToManyField('self', related_name='related')
+    related = models.ManyToManyField('self', related_name='related', blank=True)
 
     objects = DocumentManager()