fix(x/distribution): add nil check in Params.ValidateBasic

[n0b0dyCN]

Description

This change fixes a scenario in which Params.Validate() would panic when given a nil CommunityTax.

Fixes #17235

---

Author Checklist

All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.

I have...

• included the correct type prefix in the PR title
• added ! to the type prefix if API or client breaking change
• targeted the correct branch (see PR Targeting)
• provided a link to the relevant issue or specification
• followed the guidelines for building modules
• included the necessary unit and integration tests
• added a changelog entry to CHANGELOG.md
• included comments for documenting Go code
• updated the relevant documentation or specification
• reviewed "Files changed" and left comments if necessary
• run make lint and make test
• confirmed all CI checks have passed

Reviewers Checklist

All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.

I have...

• confirmed the correct type prefix in the PR title
• confirmed ! in the type prefix if API or client breaking change
• confirmed all author checklist items have been addressed
• reviewed state machine logic
• reviewed API design and naming
• reviewed documentation is accurate
• reviewed tests and test coverage
• manually tested (if applicable)

[julienrbrt]

Hi! Could you add a test?

[julienrbrt]

Why not using just doing return validateCommunityTax(p.CommunityTax) instead?

[n0b0dyCN]

That's a good idea. I'll add an update

[julienrbrt]

Awesome, thank you! Could you add a changelog entry under unreleased bug fixes?

[n0b0dyCN]

Using function validateCommunityTax in Params.ValidateBasic and add test case.
I'm new to Golang and not sure if there is a better way to initiate the Params struct with nil field other than using Unmarshal.

[julienrbrt]

Using function validateCommunityTax in Params.ValidateBasic and add test case. I'm new to Golang and not sure if there is a better way to initiate the Params struct with nil field other than using Unmarshal.

You could add the following test case in TestParams_ValidateBasic instead of your extra test:

{"community tax nil", fields{sdkmath.LegacyDec{}, toDec("0"), toDec("0"), false}, true},

[n0b0dyCN]

Both test case and change log is updated.

[julienrbrt]

Could you update the integration tests?

cosmos-sdk/tests/integration/distribution/keeper/msg_server_test.go

Line 659 in 31f7247

func TestMsgUpdateParams(t *testing.T) {