Description of problem:
When moving 3 hosts to maintenance the following error message appears twice:

2014-07-01 19:43:40,743 ERROR [org.ovirt.engine.core.vdsbroker.VdsUpdateRunTimeInfo] (DefaultQuartzScheduler_Worker-80) [143139cd] Host encounter a problem moving to maintenance mode, probably error during disconn
ecting it from pool java.lang.NullPointerException. The Host will stay in Maintenance
2014-07-01 19:43:44,251 INFO  [org.ovirt.engine.core.vdsbroker.vdsbroker.DisconnectStoragePoolVDSCommand] (DefaultQuartzScheduler_Worker-93) FINISH, DisconnectStoragePoolVDSCommand, log id: 2216e000
2014-07-01 19:43:44,252 ERROR [org.ovirt.engine.core.bll.CommandsFactory] (DefaultQuartzScheduler_Worker-93) Cant find constructor for type org.ovirt.engine.core.bll.storage.DisconnectHostFromStoragePoolServersCommand with parameter types: [class org.ovirt.engine.core.common.action.HostStoragePoolParametersBase]
2014-07-01 19:43:44,252 ERROR [org.ovirt.engine.core.bll.CommandsFactory] (DefaultQuartzScheduler_Worker-93) An exception has occured while trying to create a command object for command DisconnectHostFromStoragePoolServers: java.lang.RuntimeException: could not find matching constructor for Command class class org.ovirt.engine.core.bll.storage.DisconnectHostFromStoragePoolServersCommand
        at org.ovirt.engine.core.bll.CommandsFactory.findCommandConstructor(CommandsFactory.java:197) [bll.jar:]
        at org.ovirt.engine.core.bll.CommandsFactory.createCommand(CommandsFactory.java:61) [bll.jar:]
        at org.ovirt.engine.core.bll.Backend.runActionImpl(Backend.java:410) [bll.jar:]
        at org.ovirt.engine.core.bll.Backend.runInternalAction(Backend.java:360) [bll.jar:]
        at sun.reflect.GeneratedMethodAccessor279.invoke(Unknown Source) [:1.7.0_60]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) [rt.jar:1.7.0_60]
        at java.lang.reflect.Method.invoke(Method.java:606) [rt.jar:1.7.0_60]
        at org.jboss.as.ee.component.ManagedReferenceMethodInterceptorFactory$ManagedReferenceMethodInterceptor.processInvocation(ManagedReferenceMethodInterceptorFactory.java:72) [jboss-as-ee-7.3.0.Final-redhat-14.jar:7.3.0.Final-redhat-14]

Version-Release number of selected component (if applicable):
ovirt-engine-3.5 git hash: 0b16ed7

How reproducible:
100%

Steps to Reproduce:
1. Have three hosts in a data center
2. Move to maintenance the hosts one by one starting from the SPM

Actual results:
The command fails with the error mentioned above.

Expected results:
DisconnectHostFromStoragePoolServersCommand should continue normally.

Additional info:
I have the feeling that this could be related to the fact that I am moving to maintenance multiple hosts at the same time starting from the SPM. It seems that moving a single host to maintenance didn't expose the problem.