fix(mapping): call fillSliceValue panic if the value is nil (#3839)

core/mapping/unmarshaler.go

@@ -249,6 +249,9 @@ func (u *Unmarshaler) fillSliceFromString(fieldType reflect.Type, value reflect.
 
 func (u *Unmarshaler) fillSliceValue(slice reflect.Value, index int,
 	baseKind reflect.Kind, value any, fullName string) error {
+	if value == nil {
+		return errUnsupportedType
+	}
 	ithVal := slice.Index(index)
 	switch v := value.(type) {
 	case fmt.Stringer:

core/mapping/unmarshaler_test.go

@@ -1329,6 +1329,20 @@ func TestUnmarshalInt64Slice(t *testing.T) {
 	}
 }
 
+func TestUnmarshalNullableSlice(t *testing.T) {
+	var v struct {
+		Ages  []int64 `key:"ages"`
+		Slice []int8  `key:"slice"`
+	}
+	m := map[string]any{
+		"ages":  []int64{1, 2},
+		"slice": `[null,2]`,
+	}
+
+	ast := assert.New(t)
+	ast.Equal(UnmarshalKey(m, &v), errUnsupportedType)
+}
+
 func TestUnmarshalIntSlice(t *testing.T) {
 	var v struct {
 		Ages  []int `key:"ages"`