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GraphQL API Attribute not removed when providing null

See original GitHub issue

Describe the bug When doing an update mutation with a value of null (or undefined) for the key the attribute is not removed in DynamoDB.

To Reproduce Steps to reproduce the behavior: Create a model and push it and generate the graphql mutations

type Article @model 
{
  id: ID!
  title: String
  subtitle: String
}

Insert an article with a title and subtitle

Do an update mutation with a new title and set subtitle to null

graphqlOperation(mutations.updateArticle, {
   input: { title: 'new title', subtitle: null },
})

The title is changed in DynamoDB but the subtitle is still there untouched

Expected behavior What was expected is that the attribute subtitle should be removed from the DynamoDB table. This is mentioned/documented on the AppSync docs

If the attribute is set to null, it asks AWS AppSync and DynamoDB to remove that attribute from the post object

When executing the query in the AppSync console the attribute was removed (as expected)

mutation UpdateArticle {
  updateArticle(input: { id: "4f482b...", title: "new title", subtitle: null }) {
    id
  }
}

Also in the generated mutation resolver (generende with Amplify CLI) of the article there you see the line where it states when the value is null the key (attribute) should be removed

#if( $util.isNull($entry.value) )
    #set( $discard = $expRemove.add("#$entry.key") )
    $util.qr($expNames.put("#$entry.key", "$entry.key"))

Desktop:

OS: MacOS X
Browser Safari, Chrome, Firefox
Latest version

Additional context Updated all amplify packages to latest with no effect, also tried to do it with the Appsync SDK and Client but no change; also with a own typed gql no change.

dependencies": {
    "aws-amplify": "^1.1.18",
    "aws-amplify-react": "^2.2.5",
    "aws-appsync": "^1.7.0",
    "graphql-tag": "^2.10.0",
    "node-sass": "^4.11.0",
    "npm": "^6.5.0",
    "prop-types": "^15.6.2",
    "react": "^16.7.0",
    "react-dom": "^16.7.0",
    "react-scripts": "^2.1.3"
  }