code: def appendMissingSignatures(self):
          
          missing_signatures = self.get("missing_signatures", [])
          for pub in missing_signatures:
              wif = self.blockchain.wallet.getPrivateKeyForPublicKey(pub)
              if wif:
                  self.appendWif(wif)
docs: Store which accounts/keys are supposed to sign the transaction
  
              This method is used for an offline-signer!