Jbpm 4.2 集成Spring问题 Error creating bean with name 'processEngine'

Jbpm 4.2 集成Spring问题 Error creating bean with name 'processEngine'

使用Jbpm4.2 集成Spring 出现问题：
  
   2009-11-12 15:49:51,640 ERROR [org.springframework.web.context.ContextLoader] - Context initialization failed
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'processEngine' defined in file [......\WEB-INF\classes\spring\applicationContext-jbpm.xml]: Instantiation of bean failed; nested exception is org.springframework.beans.factory.BeanDefinitionStoreException: Factory method [public org.jbpm.api.ProcessEngine org.jbpm.pvm.internal.cfg.SpringConfiguration.buildProcessEngine()] threw exception; nested exception is java.lang.NullPointerException

  Caused by: java.lang.NullPointerException
 at org.jbpm.pvm.internal.cfg.ProcessEngineImpl.checkDb(ProcessEngineImpl.java:177)

 userCommandService 为null

  经调试发现，使用Spring后userCommandService 确实是null，
  配置中缺少什么东西？未知。 文档中并无特殊说明，
 4.1没有出现问题~ 
 应该是4.2的Bug