Make person field for PDFFile optional

(cherry picked from commit d4cc128a)

aleksis/core/migrations/0020_pdf_file_person_optional.py

+# Generated by Django 3.2.4 on 2021-07-24 13:14
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('core', '0019_fix_uniqueness_per_site'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='pdffile',
+            name='person',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.CASCADE, related_name='pdf_files', to='core.person', verbose_name='Owner'),
+        ),
+    ]

aleksis/core/models.py

@@ -1037,7 +1037,12 @@ class PDFFile(ExtensibleModel):
         return timezone.now() + timedelta(minutes=get_site_preferences()["general__pdf_expiration"])
 
     person = models.ForeignKey(
-        to=Person, on_delete=models.CASCADE, verbose_name=_("Owner"), related_name="pdf_files"
+        to=Person,
+        on_delete=models.CASCADE,
+        blank=True,
+        null=True,
+        verbose_name=_("Owner"),
+        related_name="pdf_files",
     )
     expires_at = models.DateTimeField(
         verbose_name=_("File expires at"), default=_get_default_expiration