fix: null guard for tx fee amounts (backport cosmos#10327) (cosmos#10342

)

* fix: null guard for tx fee amounts (cosmos#10327)

## Description

It is possible to submit a TX with a fees object containing a Coin with a nil amount. This results in a rather cryptic redacted panic response when the basic validation checks fee Coins for negative amounts.

This PR adds an additional check for nil to provide a friendlier error message.

---

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- [x] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] added `!` to the type prefix if API or client breaking change
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- [x] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#testing) (note: First PR against the SDK so please comment with what needs to be done)
- [x] added a changelog entry to `CHANGELOG.md`
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- [ ] updated the relevant documentation or specification
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- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed `!` in the type prefix if API or client breaking change
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(cherry picked from commit 96e162b)

# Conflicts:
#	CHANGELOG.md

* solve conflicts

* move sections

Co-authored-by: Alex Megalokonomos <[email protected]>
Co-authored-by: marbar3778 <[email protected]>

CHANGELOG.md

@@ -41,6 +41,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 ### Improvements
 
 * [\#10262](https://github.com/cosmos/cosmos-sdk/pull/10262) Remove unnecessary logging in `x/feegrant` simulation.
+* [\#10327](https://github.com/cosmos/cosmos-sdk/pull/10327) Add null guard for possible nil `Amount` in tx fee `Coins`
 
 ### Bug Fixes
 

types/coin.go

@@ -181,7 +181,7 @@ func (coin Coin) IsNegative() bool {
 
 // IsNil returns true if the coin amount is nil and false otherwise.
 func (coin Coin) IsNil() bool {
-	return coin.Amount.BigInt() == nil
+	return coin.Amount.i == nil
 }
 
 //-----------------------------------------------------------------------------

types/coin_test.go

@@ -1319,6 +1319,7 @@ func (s *coinTestSuite) TestCoinsIsAnyNil() {
 	s.Require().True(sdk.Coins{twoAtom, nilAtom, fiveAtom, threeEth}.IsAnyNil())
 	s.Require().True(sdk.Coins{nilAtom, twoAtom, fiveAtom, threeEth}.IsAnyNil())
 	s.Require().False(sdk.Coins{twoAtom, fiveAtom, threeEth}.IsAnyNil())
+
 }
 
 func (s *coinTestSuite) TestMarshalJSONCoins() {

types/tx/types.go

@@ -66,7 +66,7 @@ func (t *Tx) ValidateBasic() error {
 	}
 
 	if fee.Amount.IsAnyNil() {
-		return errorsmod.Wrapf(
+		return sdkerrors.Wrapf(
 			sdkerrors.ErrInsufficientFee,
 			"invalid fee provided: null",
 		)