HTMLFile: make md5 field nullable (#8025)

This is so we can delete it safely in the next release.

Author: stsewd

readthedocs/projects/migrations/0070_make_md5_field_nullable.py

@@ -0,0 +1,18 @@
+# Generated by Django 2.2.19 on 2021-03-17 15:23
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('projects', '0069_migrate_protected_projects'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='importedfile',
+            name='md5',
+            field=models.CharField(max_length=255, null=True, verbose_name='MD5 checksum'),
+        ),
+    ]

readthedocs/projects/models.py

@@ -1366,7 +1366,7 @@ class ImportedFile(models.Model):
     # of 4096 characters for most filesystems (including EXT4).
     # https://github.com/rtfd/readthedocs.org/issues/5061
     path = models.CharField(_('Path'), max_length=4096)
-    md5 = models.CharField(_('MD5 checksum'), max_length=255)
+    md5 = models.CharField(_('MD5 checksum'), max_length=255, null=True)
     commit = models.CharField(_('Commit'), max_length=255)
     build = models.IntegerField(_('Build id'), null=True)
     modified_date = models.DateTimeField(_('Modified date'), auto_now=True)