Never return fields not saved in Dynamo on create

If an object containing undefined was provided to create then this
undefined field would be returned but not on read. This was confusing.

This guarantees that we treat them the same.

src/index.test.ts

@@ -240,7 +240,6 @@ describe("omanyd", () => {
 
       expect(savedThing).toStrictEqual({
         id: savedThing.id,
-        value: undefined,
       });
     });
   });

src/index.ts

@@ -27,8 +27,8 @@ export function define<T>(options: Options) {
   return {
     async create(obj: Omit<T, "id"> | T): Promise<T> {
       const validated: T = await validator.validateAsync(obj);
-      await t.create(validated);
-      return validated;
+      const result = await t.create(validated);
+      return (result as unknown) as T;
     },
 
     async put(obj: T): Promise<T> {

src/table.ts

@@ -130,24 +130,26 @@ export default class Table {
     });
   }
 
-  async create(obj: PlainObject): Promise<AWS.DynamoDB.PutItemOutput> {
+  async create(obj: PlainObject): Promise<PlainObject> {
+    const serializedItem = this.serializer.toDynamoMap(obj);
     return new Promise((res, rej) => {
       this.dynamoDB.putItem(
         {
           TableName: this.options.name,
-          Item: this.serializer.toDynamoMap(obj),
+          Item: serializedItem,
         },
         (err, data) => {
           if (err) {
             return rej(err);
           }
-          return res(data);
+          // Serializing can drop undefined fields so return the deserialized serialized item
+          return res(this.deserializer.fromDynamoMap(serializedItem));
         }
       );
     });
   }
 
-  async getByHashKey(hashKey: string): Promise<Object | null> {
+  async getByHashKey(hashKey: string): Promise<PlainObject | null> {
     return new Promise((res, rej) => {
       this.dynamoDB.getItem(
         {
@@ -208,7 +210,7 @@ export default class Table {
     });
   }
 
-  async getByIndex(name: string, hashKey: string): Promise<Object | null> {
+  async getByIndex(name: string, hashKey: string): Promise<PlainObject | null> {
     const indexDefintion = (this.options.indexes ?? []).find(
       (index) => index.name === name
     );