Before You File a Bug Report Please Confirm You Have Done The Following...

• I have tried restarting my IDE and the issue persists.
• I have updated to the latest version of the packages.
• I have searched for related issues and found none that matched my issue.
• I have read the FAQ and my problem is not listed.

Playground Link

https://typescript-eslint.io/play/#ts=5.7.2&fileType=.ts&code=JYOwLgpgTgZghgYwgAgEIHsAeyDeAoZZANzgBsBXCALmQGcwpQBzAbjwF888ATCBUuFBQxyIBGGDoQyJhDAAxMqQBGiANYZMACgCUNTWx58BQ5Ain1kveOVJhN%2BrMgA%2ByUddARuh63Fv2nZ1dZBSVVBA0sXTYAehjCBMSAPyS8OOQABSEYaDdaZmQQW1JgWgALM3QyCFoEAvQAB2g4MHQoZAA6Lq5ff01kAH4rCBs7fpoQxVIVdU1otPiAOXRkaCg25CotIA&eslintrc=N4KABGBEBOCuA2BTAzpAXGUEKQAIBcBPABxQGNoBLY-AWhXkoDt8B6Y6RAM0WlqYSNkAC1pkA9gEMkyMswDm6KL2jjokcGAC%2BILUA&tsconfig=N4KABGBEDGD2C2AHAlgGwKYCcDyiAuysAdgM6QBcYoEEkJemy0eAcgK6qoDCAFutAGsylBm3TgwAXxCSgA&tokens=false

Repro Code

interface Box {
  value: string;
}

declare function getFallbackBox(): Box;

declare const defaultBox: Box | undefined;

defaultBox || getFallbackBox();
//         ~~
// Prefer using nullish coalescing operator ...

defaultBox ? defaultBox : getFallbackBox();
// No error :(

ESLint Config

module.exports = {
  "rules": {
    "@typescript-eslint/prefer-nullish-coalescing": "error"
  }
}

tsconfig

{
  "compilerOptions": {
    "strictNullChecks": true
  }
}

Expected Result

Both the || or and the ?: ternary should report.

Actual Result

Only the || or reports.

Additional Info

Ternary support was added in #4905, but seems limited to more strict cases of both undefined and null being checked?

Split out of #10218 (comment).

💖