diff --git a/aleksis/apps/chronos/migrations/0001_initial.py b/aleksis/apps/chronos/migrations/0001_initial.py
index 892b7a0303250fb221e58d8906a49ab14fa0afe8..ac57ccce82abedae7fbfc5f3bbeb3fb964ca8f69 100644
--- a/aleksis/apps/chronos/migrations/0001_initial.py
+++ b/aleksis/apps/chronos/migrations/0001_initial.py
@@ -1,4 +1,4 @@
-# Generated by Django 3.0.5 on 2020-05-04 12:00
+# Generated by Django 3.0.5 on 2020-05-04 14:16
 
 import aleksis.apps.chronos.managers
 import calendarweek.calendarweek
@@ -112,7 +112,7 @@ class Migration(migrations.Migration):
             fields=[
                 ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                 ('extended_data', django.contrib.postgres.fields.jsonb.JSONField(default=dict, editable=False)),
-                ('weekday', models.PositiveSmallIntegerField(choices=[(0, 'Montag'), (1, 'Dienstag'), (2, 'Mittwoch'), (3, 'Donnerstag'), (4, 'Freitag'), (5, 'Samstag'), (6, 'Sonntag')], verbose_name='Week day')),
+                ('weekday', models.PositiveSmallIntegerField(choices=[(0, 'Monday'), (1, 'Tuesday'), (2, 'Wednesday'), (3, 'Thursday'), (4, 'Friday'), (5, 'Saturday'), (6, 'Sunday')], verbose_name='Week day')),
                 ('period', models.PositiveSmallIntegerField(verbose_name='Number of period')),
                 ('time_start', models.TimeField(verbose_name='Start time')),
                 ('time_end', models.TimeField(verbose_name='End time')),
@@ -232,7 +232,7 @@ class Migration(migrations.Migration):
                 ('week', models.IntegerField(default=calendarweek.calendarweek.CalendarWeek.current_week, verbose_name='Week')),
                 ('cancelled', models.BooleanField(default=False, verbose_name='Cancelled?')),
                 ('cancelled_for_teachers', models.BooleanField(default=False, verbose_name='Cancelled for teachers?')),
-                ('comment', models.TextField(blank=True, verbose_name='Comment')),
+                ('comment', models.TextField(blank=True, null=True, verbose_name='Comment')),
                 ('lesson_period', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='substitutions', to='chronos.LessonPeriod', verbose_name='Lesson period')),
                 ('room', models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.CASCADE, to='chronos.Room', verbose_name='Room')),
                 ('site', models.ForeignKey(default=1, editable=False, on_delete=django.db.models.deletion.CASCADE, to='sites.Site')),
@@ -288,7 +288,7 @@ class Migration(migrations.Migration):
                 ('title', models.CharField(max_length=255, verbose_name='Title')),
                 ('date_start', models.DateField(null=True, verbose_name='Start date')),
                 ('date_end', models.DateField(null=True, verbose_name='End date')),
-                ('comments', models.TextField(blank=True, verbose_name='Comments')),
+                ('comments', models.TextField(blank=True, null=True, verbose_name='Comments')),
                 ('site', models.ForeignKey(default=1, editable=False, on_delete=django.db.models.deletion.CASCADE, to='sites.Site')),
             ],
             options={
@@ -303,7 +303,7 @@ class Migration(migrations.Migration):
                 ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                 ('extended_data', django.contrib.postgres.fields.jsonb.JSONField(default=dict, editable=False)),
                 ('week', models.IntegerField(default=calendarweek.calendarweek.CalendarWeek.current_week, verbose_name='Week')),
-                ('comment', models.CharField(blank=True, max_length=255, verbose_name='Comment')),
+                ('comment', models.CharField(blank=True, max_length=255, null=True, verbose_name='Comment')),
                 ('groups', models.ManyToManyField(related_name='extra_lessons', to='core.Group', verbose_name='Groups')),
                 ('period', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='extra_lessons', to='chronos.TimePeriod', verbose_name='Time period')),
                 ('room', models.ForeignKey(null=True, on_delete=django.db.models.deletion.CASCADE, related_name='extra_lessons', to='chronos.Room', verbose_name='Room')),
@@ -324,7 +324,7 @@ class Migration(migrations.Migration):
                 ('extended_data', django.contrib.postgres.fields.jsonb.JSONField(default=dict, editable=False)),
                 ('date', models.DateField(null=True, verbose_name='Date of exam')),
                 ('title', models.CharField(max_length=255, verbose_name='Title')),
-                ('comment', models.TextField(blank=True, verbose_name='Comment')),
+                ('comment', models.TextField(blank=True, null=True, verbose_name='Comment')),
                 ('lesson', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='exams', to='chronos.Lesson', verbose_name='Lesson')),
                 ('period_from', models.ForeignKey(null=True, on_delete=django.db.models.deletion.CASCADE, related_name='+', to='chronos.TimePeriod', verbose_name='Start period')),
                 ('period_to', models.ForeignKey(null=True, on_delete=django.db.models.deletion.CASCADE, related_name='+', to='chronos.TimePeriod', verbose_name='End period')),
@@ -344,7 +344,7 @@ class Migration(migrations.Migration):
             fields=[
                 ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                 ('extended_data', django.contrib.postgres.fields.jsonb.JSONField(default=dict, editable=False)),
-                ('title', models.CharField(blank=True, max_length=255, verbose_name='Title')),
+                ('title', models.CharField(blank=True, max_length=255, null=True, verbose_name='Title')),
                 ('date_start', models.DateField(null=True, verbose_name='Start date')),
                 ('date_end', models.DateField(null=True, verbose_name='End date')),
                 ('groups', models.ManyToManyField(related_name='events', to='core.Group', verbose_name='Groups')),
@@ -382,7 +382,7 @@ class Migration(migrations.Migration):
                 ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                 ('extended_data', django.contrib.postgres.fields.jsonb.JSONField(default=dict, editable=False)),
                 ('short_name', models.CharField(max_length=255, verbose_name='Short name')),
-                ('name', models.CharField(blank=True, max_length=255, verbose_name='Name')),
+                ('name', models.CharField(blank=True, max_length=255, null=True, verbose_name='Name')),
                 ('site', models.ForeignKey(default=1, editable=False, on_delete=django.db.models.deletion.CASCADE, to='sites.Site')),
             ],
             options={
@@ -400,7 +400,7 @@ class Migration(migrations.Migration):
                 ('extended_data', django.contrib.postgres.fields.jsonb.JSONField(default=dict, editable=False)),
                 ('date_start', models.DateField(null=True, verbose_name='Start date')),
                 ('date_end', models.DateField(null=True, verbose_name='End date')),
-                ('comment', models.TextField(blank=True, verbose_name='Comment')),
+                ('comment', models.TextField(blank=True, null=True, verbose_name='Comment')),
                 ('group', models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.CASCADE, related_name='absences', to='core.Group', verbose_name='Group')),
                 ('period_from', models.ForeignKey(null=True, on_delete=django.db.models.deletion.CASCADE, related_name='+', to='chronos.TimePeriod', verbose_name='Start period')),
                 ('period_to', models.ForeignKey(null=True, on_delete=django.db.models.deletion.CASCADE, related_name='+', to='chronos.TimePeriod', verbose_name='End period')),