fix(client): don't panic on marshal with extra null field

Author: stainless-app[bot]

internal/apijson/decoder.go

@@ -461,7 +461,7 @@ func (d *decoderBuilder) newStructTypeDecoder(t reflect.Type) decoderFunc {
 			}
 
 			// Handle null [param.Opt]
-			if itemNode.Type == gjson.Null && dest.Type().Implements(reflect.TypeOf((*param.Optional)(nil)).Elem()) {
+			if itemNode.Type == gjson.Null && dest.IsValid() && dest.Type().Implements(reflect.TypeOf((*param.Optional)(nil)).Elem()) {
 				dest.Addr().Interface().(json.Unmarshaler).UnmarshalJSON([]byte(itemNode.Raw))
 				continue
 			}

internal/apijson/decoderesp_test.go

@@ -0,0 +1,30 @@
+package apijson_test
+
+import (
+	"encoding/json"
+	"github.com/carbon-aware/scheduler-client-golang/internal/apijson"
+	"github.com/carbon-aware/scheduler-client-golang/packages/respjson"
+	"testing"
+)
+
+type StructWithNullExtraField struct {
+	Results []string `json:"results,required"`
+	JSON    struct {
+		Results     respjson.Field
+		ExtraFields map[string]respjson.Field
+		raw         string
+	} `json:"-"`
+}
+
+func (r *StructWithNullExtraField) UnmarshalJSON(data []byte) error {
+	return apijson.UnmarshalRoot(data, r)
+}
+
+func TestDecodeWithNullExtraField(t *testing.T) {
+	raw := `{"something_else":null}`
+	var dst *StructWithNullExtraField
+	err := json.Unmarshal([]byte(raw), &dst)
+	if err != nil {
+		t.Fatalf("error: %s", err.Error())
+	}
+}