Error when updating a string attribute using dart sdk

AppwriteException: general_argument_invalid, Param "default" is not optional. (400)

cc: @D5 We are using dart-sdk for performing this sync

Here is a code snippet for the same:

await dest.databases.updateStringAttribute(
  databaseId: databaseId,
  collectionId: collectionId,
  key: attributeA.key,
  size: attributeA.size!,
  xrequired: attributeA.required,
  xdefault:
      attributeA.required ? null : (attributeA.defaultValue ?? ''),
);

if I write the xdefault part like this:

xdefault: attributeA.defaultValue ?? '',

I get this error:
AppwriteException: attribute_default_unsupported, Cannot set default value for required attribute (400)

Hmm I think it can't be nul as it needs to be true or false?