OneTable removes empty strings in nested objects

[brewencoded]

I noticed an issue with create/update methods where Model fields with type: Object that have empty strings are being removed unless you use the nulls: true param. For example:

// model
Test: {
  pk: { type: String, value: 'TEST#${testId}' },
  testId: { type: String, required: true },
  value: { type: Object, required: true }
}

// code
const model = table.getModel('Test');
await model.create({
  testId: 'test123',
  value: { a: 'a', b: '' }
});

would lead to an object in the table that looks like:

{
  "pk": {
    "S": "TEST#test123"
  },
  "testId": {
    "S": "test123"
  },
  "value": {
    "M": {
      "a": {
        "S": "a"
      },
    }
  }
}

The property b, ends up missing.

After reviewing the code in Model.js, I noticed the lines:
https://github.com/sensedeep/dynamodb-onetable/blob/main/src/Model.js#L1617-L1622
and
https://github.com/sensedeep/dynamodb-onetable/blob/main/src/Model.js#L1999-L2001
Which reference an old issue where DynamoDB did not support storing empty strings.

This is no longer the case as of 2020. I was using this feature in DynamoDB-Toolbox previously:
https://aws.amazon.com/about-aws/whats-new/2020/05/amazon-dynamodb-now-supports-empty-values-for-non-key-string-and-binary-attributes-in-dynamodb-tables/

At the time that code was written it may have been accurate, but now I would consider it a bug. I'm working around this with nulls: true and transform for now. Any chance we could get this code updated?

[mobsense]

If you comment those lines of code out, does it perform correctly?

[brewencoded]

I got around to creating a test that inserts an entity with an empty string field. When I comment out https://github.com/sensedeep/dynamodb-onetable/blob/main/src/Model.js#L1617-L1620 it successfully inserts the nested empty string.

[brewencoded]

I'm not sure what the exact solution is, but I think handleEmpties should respect the DynamoDBDocumentClient's marshallOptions.convertEmptyValues and then apply the nulls attribute before writing.

[mobsense]

We don't use the DynamoDBDocumentClient but go directly to the layer below.

Just committing a fix that uses:

if (this.table.params.legacyEmpties === true) {
    properties[name] = this.handleEmpties(field, value)
}

Users who need the old behavior can set "handleEmpties: true" in the schema.params.