Kit-Handler call Run.onUiSync(Func) return null

[qiujuer]

In this method, I do same thing then return a String. but the return str is null.

String ret = Run.onUiSync(new Func<String>() {
            @Override
            public String call() {
                if (mText != null)
                    mText.append("\n" + msg);
                return "LOG " + msg;
            }
        });
Log.d(tag, ret);

ret same time is null.