Add buf check.

client.go

@@ -1,6 +1,7 @@
 package deploygate
 
 import (
+	"bytes"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -113,18 +114,25 @@ func (c *Client) NewRequest(httpRequest *HttpRequest) (*http.Response, error) {
 func (c *Client) Decode(resp *http.Response, out interface{}) error {
 	defer resp.Body.Close()
 
+	buf := new(bytes.Buffer)
+	buf.ReadFrom(resp.Body)
+
 	if resp.StatusCode >= 300 {
-		return fmt.Errorf("status code is %v, body is %v", resp.StatusCode, resp.Body)
+		return fmt.Errorf("status code is %v, body is %v", resp.StatusCode, buf.String())
 	}
 
 	if resp.ContentLength == 0 {
 		return nil
 	}
 
-	err := json.NewDecoder(resp.Body).Decode(&out)
+	if buf.String() == "" {
+		return nil
+	}
+
+	err := json.Unmarshal(buf.Bytes(), &out)
 
 	if err != nil {
-		return fmt.Errorf("%v, output type is %T, body is %v", err, out, resp.Body)
+		return fmt.Errorf("%v, output type is %T, body is %v", err, out, buf.String())
 	}
 
 	return nil