fix(math): reset Int state when Unmarshal sees empty input

math/int.go

@@ -492,7 +492,14 @@ func (i *Int) MarshalTo(data []byte) (n int, err error) {
 // Unmarshal implements the gogo proto custom type interface.
 func (i *Int) Unmarshal(data []byte) error {
 	if len(data) == 0 {
-		i = nil
+		if i == nil {
+			return errors.New("cannot unmarshal Int into nil receiver")
+		}
+		if i.i == nil {
+			i.i = new(big.Int)
+		} else {
+			i.i.SetInt64(0)
+		}
 		return nil
 	}
 

math/int_test.go

@@ -692,3 +692,19 @@ func BenchmarkIntOverflowCheckTime(b *testing.B) {
 	}
 	sink = nil
 }
+
+// TestIntUnmarshalEmpty demonstrates the bug where Unmarshal with empty bytes
+// doesn't reset the Int value to zero
+func TestIntUnmarshalEmpty(t *testing.T) {
+	// Create an Int with a non-zero value
+	i := math.NewInt(12345)
+	require.Equal(t, int64(12345), i.Int64(), "initial value should be 12345")
+
+	// Unmarshal empty bytes - should reset to zero
+	err := i.Unmarshal([]byte{})
+	require.NoError(t, err)
+
+	// With the bug: i still has value 12345
+	// After fix: i should be 0
+	require.True(t, i.IsZero(), "after unmarshaling empty bytes, Int should be zero, but got: %s", i.String())
+}