typelevel/cats

Make `Hash.fromUniversalHashCode` null safe

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#4,831 opened on Feb 22, 2026

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 (6 comments) (1 reaction) (1 assignee)Scala (1,241 forks)batch import
good first issue

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Description

Similarly to how Show.fromToString have been recently made null safe (#4689 and #4790), I propose making Hash.fromUniversalHashCode also null safe. Specifically, I think it should use x.## instead of x.hashCode(). (The eqv method is already fine, as it uses ==.)

Contributor guide

Research direction
Inspect the current implementation of `Hash.fromUniversalHashCode` and understand how `x.##` handles null. Then implement the change similarly to the `Show.fromToString` null safety changes referenced in issues #4689 and #4790.
Tech stack
None
Domain
backend
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
ScalaGit
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
75