fix: change non nil relayer check to non empty (backport #1774)

[mergify]

This is an automatic backport of pull request #1774 done by Mergify.
Cherry-pick of 126ab2d has failed:

On branch mergify/bp/release/v4.0.x/pr-1774
Your branch is up to date with 'origin/release/v4.0.x'.

You are currently cherry-picking commit 126ab2d.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   modules/apps/29-fee/types/errors.go
	modified:   modules/apps/29-fee/types/fee.go
	modified:   modules/apps/29-fee/types/fee_test.go
	modified:   modules/apps/29-fee/types/msgs.go
	modified:   modules/apps/29-fee/types/msgs_test.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   CHANGELOG.md

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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