spring注入null值

使用spring配置jedis连接池，需要指定db索引，但jedis poo构造函数中需要给password也赋值，看了源码，如果password赋值null，则不再做auth，具体配置如下：

<bean id="jedisConfig" class="redis.clients.jedis.JedisPoolConfig">
        <property name="testWhileIdle" value="${redis.pool.testWhileIdle}"/>
        <property name="minEvictableIdleTimeMillis" value="${redis.pool.minEvictableIdleTimeMillis}"/>
        <property name="timeBetweenEvictionRunsMillis" value="${redis.pool.timeBetweenEvictionRunsMillis}"/>
        <property name="numTestsPerEvictionRun" value="${redis.pool.numTestsPerEvictionRun}"/>
        <property name="maxTotal" value="${redis.pool.maxTotal}" />
        <property name="maxIdle" value="${redis.pool.maxIdle}" />
        <property name="minIdle" value="${redis.pool.minIdle}" />
        <property name="testOnBorrow" value="${redis.pool.testOnBorrow}" />
        <property name="testOnReturn" value="${redis.pool.testOnReturn}" />
	</bean>
	
	<bean id="armySignInJedisPool" class="redis.clients.jedis.JedisPool" destroy-method="destroy">
        <constructor-arg ref="armySignInJedisConfig" />
        <constructor-arg value="${redis.config.ip}" />
        <constructor-arg type="int"  value="${redis.config.port}" />
        <constructor-arg type="int"  value="${redis.config.timeout}" />
        <constructor-arg type="String"><null/></constructor-arg>
        <constructor-arg type="int"  value="${redis.config.dbindex}" />
        
	</bean>