Fix Issue#3962

[a1batr0ss]

Fix Issue3962: 对于JSON.parse()，参数为空字符串时，返回值为null, 若不判空，后边代码会抛出空指针异常。

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[arjun12102019]

Fix Issue3962: 对于JSON.parse()，参数为空字符串时，返回值为null, 若不判空，后边代码会抛出空指针异常。

感謝您的發現
引入方法(JSONObject from(String text)) 呼叫 Json.parseObject(String) 和內部 pasrseObject 方法正在處理 null 或空字串。

請參閱下面的螢幕截圖以供參考