fix(接口测试): 解决接口定义导出swagger失败

--bug=1011524
--user=郭雨琦
【接口测试】-接口定义中导出全部数据为swagger格式失败
https://www.tapd.cn/55049933/bugtrace/bugs/view/1155049933001011524

backend/src/main/java/io/metersphere/api/dto/definition/parse/Swagger3Parser.java

@@ -947,7 +947,9 @@ public class Swagger3Parser extends SwaggerAbstractParser {
             } else if (bodyType.equalsIgnoreCase("RAW")) {
                 bodyInfo = new JSONObject();
                 ((JSONObject) bodyInfo).put("type", "string");
+                if (body != null && body.get("raw") != null) {
                     ((JSONObject) bodyInfo).put("example", body.get("raw").toString());
+                }
             } else if (bodyType.equalsIgnoreCase("XML")) {
                 String xmlText = body.getString("raw");
                 JSONObject xmlToJson = XMLUtils.XmlToJson(xmlText);