diff --git a/types.go b/types.go
index 8ff901f..6afe695 100644
--- a/types.go
+++ b/types.go
@@ -51,6 +51,9 @@ type APIResponse struct {
 // String dumps JSON without tailing \n
 func (resp *APIResponse) String() string {
 	sb := strings.Builder{}
+	if len(resp.Data) == 0 {
+		resp.Data = []byte(`null`)
+	}
 	err := json.NewEncoder(&sb).Encode(resp)
 	if err != nil {
 		panic(errors.Wrap(err, "unexpected"))
diff --git a/types_test.go b/types_test.go
new file mode 100644
index 0000000..41e4e16
--- /dev/null
+++ b/types_test.go
@@ -0,0 +1,18 @@
+package goba
+
+import "testing"
+
+func TestMarshalAPIResponse(t *testing.T) {
+	rsp := &APIResponse{
+		Status:  "error",
+		Data:    []byte(`null`),
+		Message: "12345",
+	}
+	t.Log(rsp.String())
+	rsp = &APIResponse{
+		Status:  "error",
+		Data:    []byte(``),
+		Message: "12345",
+	}
+	t.Log(rsp.String())
+}