fix(types): allow transaction to be `null` (#13093)

types/lib/model.d.ts

@@ -35,7 +35,7 @@ export interface Transactionable {
   /**
    * Transaction to run query under
    */
-  transaction?: Transaction;
+  transaction?: Transaction | null;
 }
 
 export interface SearchPathable {

types/test/transaction.ts

@@ -78,3 +78,9 @@ async function nestedTransact() {
   });
   await tr.commit();
 }
+
+async function excludeFromTransaction() {
+  await sequelize.transaction(async t =>
+    await sequelize.query('SELECT 1', { transaction: null })
+  );
+}