types: fix panic on Int.BigInt()

CHANGELOG.md

@@ -186,6 +186,7 @@ be used to retrieve the actual proposal `Content`. Also the `NewMsgSubmitProposa
 
 ### Bug Fixes
 
+* (types) [\#7084](https://github.com/cosmos/cosmos-sdk/pull/7084) Fix panic when calling `BigInt()` on an uninitialized `Int`.
 * (x/bank) [\#6536](https://github.com/cosmos/cosmos-sdk/pull/6536) Fix bug in `WriteGeneratedTxResponse` function used by multiple 
 REST endpoints. Now it writes a Tx in StdTx format.
 * (x/staking) [\#6529](https://github.com/cosmos/cosmos-sdk/pull/6529) Export validator addresses (previously was empty).

types/decimal.go

@@ -208,6 +208,10 @@ func (d Dec) Abs() Dec          { return Dec{new(big.Int).Abs(d.i)} } // absolut
 
 // BigInt returns a copy of the underlying big.Int.
 func (d Dec) BigInt() *big.Int {
+	if d.IsNil() {
+		return nil
+	}
+
 	copy := new(big.Int)
 	return copy.Set(d.i)
 }

types/int.go

@@ -76,9 +76,17 @@ type Int struct {
 
 // BigInt converts Int to big.Int
 func (i Int) BigInt() *big.Int {
+	if i.IsNil() {
+		return nil
+	}
 	return new(big.Int).Set(i.i)
 }
 
+// IsNil returns true if Int is uninitialized
+func (i Int) IsNil() bool {
+	return i.i == nil
+}
+
 // NewInt constructs Int from int64
 func NewInt(n int64) Int {
 	return Int{big.NewInt(n)}

types/int_test.go

@@ -81,6 +81,8 @@ func TestIntPanic(t *testing.T) {
 
 	// Division-by-zero check
 	require.Panics(t, func() { i1.Quo(NewInt(0)) })
+
+	require.NotPanics(t, func() { Int{}.BigInt() })
 }
 
 // Tests below uses randomness