Nutch-1.1异常信息:No agents listed in 'http.agent.name' property

Nutch1.1异常信息如下:

Fetcher: No agents listed in 'http.agent.name' property.
Exception in thread "main" java.lang.IllegalArgumentException: Fetcher: No agents listed in 'http.agent.name' property.
	at org.apache.nutch.fetcher.Fetcher.checkConfiguration(Fetcher.java:1161)
	at org.apache.nutch.fetcher.Fetcher.fetch(Fetcher.java:1067)
	at org.apache.nutch.crawl.Crawl.main(Crawl.java:133)

经过搜索才知道是nutch-default.xml属性设置问题:

抛出异常前的设置:

<property>
  <name>http.agent.name</name>
  <value></value>
  <description>HTTP 'User-Agent' request header. MUST NOT be empty - 
  please set this to a single word uniquely related to your organization.

  NOTE: You should also check other related properties:

	http.robots.agents
	http.agent.description
	http.agent.url
	http.agent.email
	http.agent.version

  and set their values appropriately.

  </description>
</property>

设置如下方式后,异常信息就不见了:

<property>
  <name>http.agent.name</name>
  <value>HD nutch agent</value>
  <description>HTTP 'User-Agent' request header. MUST NOT be empty - 
  please set this to a single word uniquely related to your organization.

  NOTE: You should also check other related properties:

	http.robots.agents
	http.agent.description
	http.agent.url
	http.agent.email
	http.agent.version

  and set their values appropriately.

  </description>
</property>