Support for not passing in value for Optional Embedded Collection of Strings

[lawmicha]

Describe the bug
API request is failing when not specifying a value for an optional embedded collection of strings

To Reproduce
Steps to reproduce the behavior:

1. schema

type Todo @model {
  id: ID!
  stickies: [String]
}

2. Create a Todo without any stickies, it will default to empty array [].
3. Make API call, it will create the query variables

{
  "input" : {
    "stickies" : [

    ],
    "id" : "65883374-7B84-4457-81CD-FE1314173F44"
  }
}

3. See error

{
  "data": {
    "createTodo": null
  },
  "errors": [
    {
      "path": [
        "createTodo"
      ],
      "data": null,
      "errorType": "DynamoDB:DynamoDbException",
      "errorInfo": null,
      "locations": [
        {
          "line": 2,
          "column": 3,
          "sourceName": null
        }
      ],
      "message": "Supplied AttributeValue is empty, must contain exactly one of the supported datatypes (Service: DynamoDb, Status Code: 400, Request ID: HQVD25FPEVRHJQMBCCSTO6TFFVVV4KQNSO5AEMVJF66Q9ASUAAJG)"
    }
  ]
}

Expected behavior
When there is an empty array, we should just remove it from the variables. this may be a regression for this change? #519

[lawmicha]

codegen changes were released in 4.21.4 but deprecated, to reproduce for now, use
npm install -g @aws-amplify/cli@iosCodegenWorkshop
or use latest master branch of CLI

[ruiguoamz]

Using Schema in this link: https://github.com/aws-amplify/amplify-ios/blob/15a23697452ee8ec89b7bf49412ee2092a82d919/AmplifyTestCommon/Models/NonModel/Todo.swift

[ruiguoamz]

Using

• embedded type
• CLI (4.21.4)
  the issue doesn't occur anymore.

This is how todo object (without stickies) got created based on the schema from above link
let todo = Todo(id: "1234", name: "name", description: "description", categories: [Category(name: "Category", color: Color(name: "red", red: 255, green: 0, blue: 0))], section: Section(name: "section", number: 1.0))

[lawmicha]

this was reproduced here #595