!205 fix：不使用国际化时输出消息

Merge pull request !205 from 王帅/main

mybatis-flex-core/src/main/java/com/mybatisflex/core/exception/MybatisFlexException.java

@@ -65,6 +65,9 @@ public class MybatisFlexException extends RuntimeException {
     }
 
     private String getMessage(Locale locale) {
+        if (pattern == null) {
+            return super.getMessage();
+        }
         String localizedString = pattern.getLocalizedString(locale);
         return MessageFormat.format(localizedString, arguments);
     }