bug fix

examcloud-exchange-outer-api-provider/src/main/java/cn/com/qmth/examcloud/exchange/outer/api/provider/ExamQuestionOuterServiceProvider.java

@@ -368,7 +368,11 @@ public class ExamQuestionOuterServiceProvider extends ControllerSupport implemen
      * @return
      */
     private String getImgTxt(String studentAnswer) {
-        return Jsoup.clean(studentAnswer, Whitelist.basic());
+        if (!StringUtils.isNullOrEmpty(studentAnswer)) {
+            return Jsoup.clean(studentAnswer, Whitelist.basic());
+        }
+
+        return null;
     }
 
     /**