Merge pull request #15328 from Automattic/vkarpov15/default-function-returns-undefined

types: allow default function returning undefined with DocType override

Author: vkarpov15

test/types/schema.test.ts

@@ -1746,3 +1746,12 @@ async function schemaDouble() {
   const doc = await TestModel.findOne().orFail();
   expectType<Types.Double | null | undefined>(doc.balance);
 }
+
+function defaultReturnsUndefined() {
+  const schema = new Schema<{ arr: number[] }>({
+    arr: {
+      type: [Number],
+      default: () => void 0
+    }
+  });
+}

types/schematypes.d.ts

@@ -97,7 +97,7 @@ declare module 'mongoose' {
      * The default value for this path. If a function, Mongoose executes the function
      * and uses the return value as the default.
      */
-    default?: DefaultType<T> | ((this: EnforcedDocType, doc: any) => DefaultType<T>) | null;
+    default?: DefaultType<T> | ((this: EnforcedDocType, doc: any) => DefaultType<T> | null | undefined) | null;
 
     /**
      * The model that `populate()` should use if populating this path.