update models as NullBooleanField is deprecated.

allianceauth/hrapplications/migrations/0007_auto_20200918_1412.py

@@ -0,0 +1,18 @@
+# Generated by Django 3.1.1 on 2020-09-18 14:12
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('hrapplications', '0006_remove_legacy_models'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='application',
+            name='approved',
+            field=models.BooleanField(blank=True, default=None, null=True),
+        ),
+    ]