LDAP may return null users, leading to NullPointerException during export

java.lang.NullPointerException
  at com.atlassian.bamboo.migration.stream.UserMapper.shouldExportUser(UserMapper.java:137)
  at com.atlassian.bamboo.migration.stream.UserMapper.exportData(UserMapper.java:170)
  at com.atlassian.bamboo.migration.XmlMigrator.exportXml(XmlMigrator.java:354)
  at com.atlassian.bamboo.migration.XmlMigrator$$FastClassByCGLIB$$b6578fc7.invoke(<generated>)
  at net.sf.cglib.proxy.MethodProxy.invoke(MethodProxy.java:149)
  at org.springframework.aop.framework.Cglib2AopProxy$CglibMethodInvocation.invokeJoinpoint(Cglib2AopProxy.java:694)
  at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:149)
  at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:106)
  at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
  at org.springframework.aop.framework.Cglib2AopProxy$DynamicAdvisedInterceptor.intercept(Cglib2AopProxy.java:629)
  at com.atlassian.bamboo.migration.XmlMigrator$$EnhancerByCGLIB$$27c6415e.exportXml(<generated>)
  at com.atlassian.bamboo.migration.ImportExportManagerImpl.bambooExport(ImportExportManagerImpl.java