message: refactor: remove unnecessary null checks
diff: @@ -34,16 +34,12 @@ export class TransactionSigner {
  spendingCondition.fields.forEach(field => {
  if (field.contents.type === StacksMessageType.MessageSignature) {
  - if (!transaction.auth.authType) {
  - throw Error('"transaction.auth.authType" not defined');
  - }
  -
  const signature = field.contents;
  const nextVerify = nextVerification(
  this.sigHash,
  transaction.auth.authType,
  - spendingCondition!.fee,
  - spendingCondition!.nonce,
  + spendingCondition.fee,
  + spendingCondition.nonce,
  PubKeyEncoding.Compressed, // always compressed for multisig
  signature
  );
  