diff --git a/sophon/core/migrations/0002_auto_20210405_1641.py b/sophon/core/migrations/0002_auto_20210405_1641.py
new file mode 100644
index 0000000..6095ddf
--- /dev/null
+++ b/sophon/core/migrations/0002_auto_20210405_1641.py
@@ -0,0 +1,43 @@
+# Generated by Django 3.1.7 on 2021-04-05 16:41
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('core', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='datasource',
+            name='builtin',
+            field=models.BooleanField(help_text='Whether the source is builtin in PandaSDMX or not.', verbose_name='Builtin'),
+        ),
+        migrations.AlterField(
+            model_name='datasource',
+            name='pandasdmx_id',
+            field=models.CharField(help_text='Internal id used by PandaSDMX to reference the source.', max_length=16, primary_key=True, serialize=False, verbose_name='PandaSDMX id'),
+        ),
+        migrations.AlterField(
+            model_name='datasource',
+            name='settings',
+            field=models.JSONField(help_text='Info parameter to pass to pandasdmx.add_source if the source is not builtin (see https://pandasdmx.readthedocs.io/en/latest/api.html#pandasdmx.add_source).', null=True, verbose_name='Settings'),
+        ),
+        migrations.AlterField(
+            model_name='project',
+            name='description',
+            field=models.CharField(help_text='A brief description of the project, to be displayed inthe overview.', max_length=8192, verbose_name='Project description'),
+        ),
+        migrations.AlterField(
+            model_name='project',
+            name='name',
+            field=models.CharField(help_text='The display name of the project.', max_length=512, verbose_name='Project name'),
+        ),
+        migrations.AlterField(
+            model_name='project',
+            name='sources',
+            field=models.ManyToManyField(help_text='The sources used by this project.', null=True, related_name='used_in', to='core.DataSource'),
+        ),
+    ]
diff --git a/sophon/core/models.py b/sophon/core/models.py
index 15be000..2f1ca18 100644
--- a/sophon/core/models.py
+++ b/sophon/core/models.py
@@ -55,7 +55,8 @@ class Project(models.Model):
     sources = models.ManyToManyField(
         DataSource,
         help_text="The sources used by this project.",
-        related_name="used_in"
+        related_name="used_in",
+        null=True,
     )
 
     def __str__(self):