看看大家有知道怎么从这个app.config中读取连接字符串的？
我在读取的时候提示NUll，希望高手帮忙解决一下：

app.config文件如下：
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <connectionStrings>
  <add name="ConnectionString" connectionString ="server=.;database=test;uid=sa;pwd=sa" providerName="System.Data.SqlClient=" />  
  </connectionStrings>
  <configSections>
   
  <sectionGroup name="applicationSettings" type="System.Configuration.ApplicationSettingsGroup, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" >
  <section name="PASSManager.Properties.Settings" type="System.Configuration.ClientSettingsSection, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
   
  </sectionGroup>
  </configSections>
  <applicationSettings>
   
  <PASSManager.Properties.Settings>
  <setting name="PASSManager_DBWebService_WebService" serializeAs="String">
  <value>http://localhost:3459/WebService.asmx</value>
  </setting>
  </PASSManager.Properties.Settings>
  </applicationSettings>
  <appSettings>

  <add key="ConnectionString" value ="server=.;database=test;uid=sa;pwd=sa"/>
  </appSettings>
</configuration>

我的读取方法如下：
 string connString = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;

------解决方案--------------------
到开发版块去问问吧
------解决方案--------------------
未将对象引用设置到对象的实例
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局部变量或者全局变量的问题