fix empty set object returns postgres error in update mutation (fix #1448)

[rakeshkky]

Description

What component does this PR affect?

• Server
• Console
• CLI
• Docs
• Community Content
• Build System

Requires changes from other components? If yes, please mark the components:

• Server
• Console
• CLI
• Docs
• Community Content
• Build System

Related Issue

fix #1448

Solution and Design

If collection of _set, _inc, _append, _prepend, _delete_key, _delete_elem and
_delete_at_path input objects in update mutation is empty then server returns empty response

Ex:-

mutation withEmptySet{
  update_author(
    _set: {}
    where: {name: {_eq: "clarke"}}
  ){
    affected_rows
    returning{
      id
      name
      age
    }
  }
}

Response:-

{
  "data": {
    "update_author": {
      "affected_rows": 0,
      "returning": []
    }
  }
}

Type

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Docs update
• Community content

Checklist:

• I have read the contributing guide and my code conforms to the guidelines.
• This change requires a change in the documentation.
• I have updated the documentation accordingly.
• I have added required tests.

[hasura-bot]

Review app for commit 99a63c7 deployed to Heroku: https://hge-ci-pull-1475.herokuapp.com
Docker image for server: hasura/graphql-engine:pull1475-99a63c7

[hasura-bot]

Review app for commit 988b3ce deployed to Heroku: https://hge-ci-pull-1475.herokuapp.com
Docker image for server: hasura/graphql-engine:pull1475-988b3ce

[hasura-bot]

Review app https://hge-ci-pull-1475.herokuapp.com is deleted