Messages: No result defined for action com.xxx.action.SomeAction and result input
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癥狀: action中無法正常進行跳轉.

原因: 驗證值時驗證報錯.

解決辦法:
1) 給 Action 加入 input 的結果;
2) 去除所有證驗相關的攔截器,包括默認的validation
     調試方法:在 input 中加入調試
                      <s:fielderror/>
                      <s:debug />
                      <a href="javascript:void(0);" onclick="toggleDebug('debug');return false;">[調試信息]</a>
                      可顯示下列信息:
                      Invalid field value for field "attachment". 
                      fieldErrors {attachment=[Invalid field value for field "attachment".]} 
3) Action 不再繼承自 ActionSupport(里面有 ValidationAware 接口), 而轉而只實現 Action 接口即可.