Compound global index not updated if only 1 of 2 properties passed to the update function

Describe the bug

Global index not updated if only one of 2 fields that gs is made of if passed to update function.

Maybe there are some params i'm not aware of and can amend this behavior although I still believe it should not be a default.

To Reproduce

import {Table} from 'dynamodb-onetable'

import AWS from 'aws-sdk'
const client = new AWS.DynamoDB.DocumentClient({
    region: 'ap-southeast-2',
})

const Schema = {
    version: '0.0.1',
    client,
    name: 'Schema',
    indexes: {
        primary: { hash: 'pk', sort: 'sk' },
        gs2: { hash: 'gs2pk', sort: 'gs2sk', project: 'all' },
    },
    models: {
        Model: {
            pk: { type: String, value: '${_type}#${id}' },
            sk: { type: String, value: '#' },

            id: { type: String, required: true },

            first: { type: Number, required: true, default: 0 },
            second: { type: Number, required: true, default: 0 },

            gs2pk: { type: String, value: '#First#${first}#Second#${second}' },
            gs2sk: { type: String, value: '${_type}#' },
        },
    },
    params: {
        isoDates: true,
        timestamps: true,
        createdField: 'created',
    },
}

export const table = new Table({
    client,
    name: 'MyTable',
    schema: Schema,
    logger: true,
    timestamps: true,
    partial: true,
})

const Model = table.getModel('Model')

async function main(){

   const print = async () => {
     const data = await Model.get({id:"1" }, {hidden:true})
     console.log('gs2pk', data.gs2pk, 'first', data.first, 'second', data.second) 
   }

   await Model.upsert({id:"1", first:1, second:2}, {partial:false})
   await print()
   await Model.update({id:"1", second:3})
   await print()
   await Model.update({id:"1", first:3, second:4})
   await print()
}

main()

returns

gs2pk #First#1#Second#2 first 1 second 2  # all good
gs2pk #First#1#Second#2 first 1 second 3  # goes out of sync
gs2pk #First#3#Second#4 first 3 second 4  # again all good

which means that gs2pk is out of sync

Expected behavior

The best would be to update gs2 despite not having first property passed to the update function.

At min. it would be great getting an error otherwise developer is not aware that gs is out of sync.

Environment (please complete the following information):

    "aws-sdk": "^2.1369.0",
    "dynamodb-onetable": "^2.7.1"

sensedeep / dynamodb-onetable

Compound global index not updated if only 1 of 2 properties passed to the update function #508