Comment 2 for bug 1868817

ERROR curtin:1297 Validation error: None is not of type 'string' in
 {
  "device": "disk-sda",
  "flag": "extended",
  "id": "partition-sda2",
  "multipath": null,
  "number": 2,
  "offset": 501218304,
  "size": 68218258432,
  "type": "partition"
 }
 NoneType: None

This was recently fixed in curtin,

https://code.launchpad.net/~raharper/curtin/+git/curtin/+merge/379904
https://git.launchpad.net/curtin/commit/?id=1f9c53aecd0a514103fcb571ced54a10e3b12a0e