Fix keyerror in selected_fields when a variable is not defined

[jkimbo]

Description

Fix bug with selected_fields and undefined variables

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Documentation

Issues Fixed or Closed by This PR

• Fixes Undefined variable issue in 0.77.6 #1248

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[codecov]

Codecov Report

Merging #1249 (3d6488e) into main (a559299) will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1249      +/-   ##
==========================================
+ Coverage   97.63%   97.69%   +0.06%     
==========================================
  Files          88       88              
  Lines        3382     3388       +6     
  Branches      496      498       +2     
==========================================
+ Hits         3302     3310       +8     
+ Misses         44       43       -1     
+ Partials       36       35       -1     

[patrick91]

🚢

[botberry]

Thanks for adding the RELEASE.md file!

Here's a preview of the changelog:

---

Fixes a bug with the selected_fields property on info when an operation
variable is not defined.

Issue #1248.

---

Here's the preview release card for twitter:

Here's the tweet text:

🆕 Release (next) is out! Thanks to @ignormies for the PR 👏

Get it here 👉 https://github.com/strawberry-graphql/strawberry/releases/tag/(next)