字符串是否为空完善

scommons/src/main/java/com/xhkjedu/utils/N_Utils.java

      * @author WN
      */
     public static boolean isNotEmpty(Object obj) {
-        if (null == obj || "".equals(obj.toString().trim())) {
+        if (null == obj || "".equals(obj.toString().trim()) || "null".equals(obj.toString().trim())) {
             return false;
         } else {
             return true;