Decrypting backup file not populating xPrivKey

[vctt94]

Describe the bug

A user is reporting decrypting an old generated backup file, which when decrypting using https://bitwiseshiftleft.github.io/sjcl/demo/ it does not populate the xPrivKey. These are all the generated file:

{
	"network": "",
	"xPubKey"
	"requestPrivKey"
	"requestPubKey"
	"copayerId"
	"publicKeyRing": [{
		"xPubKey"
		"requestPubKey"
	}],
	"walletId"
	"walletName"
	"m": 
	"n": 
	"walletPrivKey"
	"personalEncryptingKey",
	"sharedEncryptingKey"
	"copayerName"
	"entropySource"
	"mnemonicHasPassphrase": false,
	"derivationStrategy": "BIP44",
	"account": 0,
	"addressType": "P2PKH"
}

To Reproduce
Steps to reproduce the behavior:

1 - decrypting file with the given website or using some sjcl tool
2 - it will not give the xPrivKey

Expected behavior

That the xPrivKey is generated and make it possible to recover the wallet.

Additional context

How can one recover an old web wallet without this information?