当freemarker中EL表达式的值为空时出现异常的解决方法

<#list pageView.list as msg>
     <form name="msgForm" id="msgForm" action="findMsgById.do"
           method="post">
        <tr class="tr3"  
            onMouseOver="this.style.backgroundColor='whitesmoke'"
            onMouseOut="this.style.backgroundColor='white'">
            <td align="center">
                <span class="style_blue_tableline">${msg_index+1
                </span>
            </td>
            <td align="center">
                <span class="style_blue_tableline">
                    <a id="editmsg" name="editmsg"
         style="cursor:pointer;color:blue;text-decoration: underline">
                       修改
                        </a>
                </span>
                <span class="style_blue_tableline">
                   <a href="logicDelMsg.do?
                      messageId=${msg.messageId}"             
                    >         删除
                      </a>
                </span>
          </td>
          <input type="hidden" id="messageId" name="messageId" 
                 value="${msg.messageId}" />
          <td align="center">
             <span class="style_blue_tableline">${msg.title}nbsp;
             </span>
          </td>
          <td align="center">
               <span class="style_blue_tableline">
                     ${msg.messageContent}&nbsp;
                </span>
           </td>
           <td align="center">
               <span class="style_blue_tableline">
                  ${msg.sendTime?string("yyyy-MM-dd HH:mm:ss")}&nbsp;
               </span>
           </td>
           <td align="center">
               <span class="style_blue_tableline">
                    ${msg.sender}&nbsp;
               </span>
           </td>
     
       </tr>
     </form>
</#list>


如以上所示，如果EL表达式中的值为空，则会报如下异常：

the expression msg.title is undefine ....


原因是：freemarker不像jsp那样，可以在页面上自动处理空值。

这时，应该将每个EL表达式改成如下：

${(msg.title)?default("")}

表示：如果这个值为空，则给一个默认值。

默认值可任意指定。