fix: add missing nil checks

[170210]

Description

There are multiple functions in the codebase missing nil checks and this PR fixed them.

This pr cherry-pick the following upstream prs

• https://github.com/cosmos/cosmos-sdk/pull/15691
• https://github.com/cosmos/cosmos-sdk/pull/12903

Motivation and context

How has this been tested?

Screenshots (if appropriate):

Checklist:

• [x] I followed the contributing guidelines and code of conduct.
• [x] I have added a relevant changelog to CHANGELOG.md
• [x] I have added tests to cover my changes.
• [ ] I have updated the documentation accordingly.
• [ ] I have updated API documentation client/docs/swagger-ui/swagger.yaml

[CLAassistant]

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1 out of 3 committers have signed the CLA.

:white_check_mark: 170210
:x: odeke-em
:x: yun-yeo
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[codecov[bot]]

Codecov Report

Attention: Patch coverage is 71.42857% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 70.43%. Comparing base (b1c09cf) to head (f42103d).

:exclamation: Current head f42103d differs from pull request most recent head 3bea915. Consider uploading reports for the commit 3bea915 to get more accurate results

Additional details and impacted files

[](https://app.codecov.io/gh/Finschia/finschia-sdk/pull/1299?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Finschia) ```diff @@ Coverage Diff @@ ## main #1299 +/- ## ========================================== - Coverage 70.43% 70.43% -0.01% ========================================== Files 643 643 Lines 54720 54724 +4 ========================================== + Hits 38542 38544 +2 - Misses 14008 14009 +1 - Partials 2170 2171 +1 ``` | [Files](https://app.codecov.io/gh/Finschia/finschia-sdk/pull/1299?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Finschia) | Coverage Δ | | |---|---|---| | [types/coin.go](https://app.codecov.io/gh/Finschia/finschia-sdk/pull/1299?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Finschia#diff-dHlwZXMvY29pbi5nbw==) | `94.72% <100.00%> (+0.02%)` | :arrow_up: | | [types/dec\_coin.go](https://app.codecov.io/gh/Finschia/finschia-sdk/pull/1299?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Finschia#diff-dHlwZXMvZGVjX2NvaW4uZ28=) | `78.24% <60.00%> (-0.52%)` | :arrow_down: | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/Finschia/finschia-sdk/pull/1299/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Finschia)