Resolution:
In SPM 1.2.0, Sometimes you can see below exceptions :
{{{
2009-11-04 16:30:45,255 [TIBCO EMS Session Dispatcher (6754)] rules.metricspublisher.AMSGRuleFunctions ERROR - Error publishing node JVM info to db
java.lang.NullPointerException
    at com.tibco.matrix.servicegrid.monitoring.rules.metricspublisher.AMSGRuleFunctions.o00000(AMSGRuleFunctions.java:628)
    at com.tibco.matrix.servicegrid.monitoring.rules.metricspublisher.AMSGRuleFunctions.o00000(AMSGRuleFunctions.java:933)
    at com.tibco.matrix.servicegrid.monitoring.rules.metricspublisher.AMSGRuleFunctions.new(AMSGRuleFunctions.java:893)
    at com.tibco.matrix.servicegrid.monitoring.rules.metricspublisher.AMSGRuleFunctions.publishNodeOrEngineData(AMSGRuleFunctions.java:864)
    at be.gen.Rules.AgentRuleSet.AMSGJVMInfoRule$AMSGJVMInfoRule_a.execute(AMSGJVMInfoRule.java:57)
    at com.tibco.cep.kernel.core.rete.ReteWM.resolveConflict(ReteWM.java:258)
    at com.tibco.cep.kernel.core.rete.ReteWM.assertObject(ReteWM.java:841)
    at com.tibco.cep.runtime.session.impl.RuleSessionImpl.assertObject(RuleSessionImpl.java:787)
    at com.tibco.cep.runtime.scheduler.impl.WorkerBasedController.executeTask(WorkerBasedController.java:135)
    at com.tibco.cep.runtime.scheduler.impl.WorkerBasedController.processEvent(WorkerBasedController.java:113)
    at com.tibco.cep.runtime.channel.impl.AbstractDestination.onMessage(AbstractDestination.java:223)

}}}
  
    It is becauses there are unwanted node send message to the queue activematrix.stats.&ltAMX_CLUSTER_NAME>.
    The steps to trouble shoot.
1. Mointor queue activematrix.stats.&ltAMX_CLUSTER_NAME> with tibemsmonitor.
    &ltEMS_HOME>/bin/tibemsmonitor -monitor $sys.monitor.Q.r.activematrix.stats.&ltAMX_CLUSTER_NAME>.
2. Should find message like below :
    {{{
messasage={Header={ JMSDestination={QUEUE:'activematrix.stats.spm_amx'} JMSDeliveryMode={NON_PERSISTENT} JMSPriority={5} JMSMessageID={ID:EmsAdmDev3.52C84A5F26A9F49:87560} JMSTimestamp={Thu Nov 12 17:13:30 2009} JMSExpiration={Thu Nov 12 17:13:45 2009}} Properties={} Body={string:'<?xml version="1.0" encoding="UTF-8"?>
&ltxmi:XMI xmi:version="2.0" xmlns:xmi="http://www.omg.org/XMI" xmlns:base="http://xsd.tns.tibco.com/corona/eventformat/basemodel" xmlns:machineinfoeventmodel="http://xsd.tns.tibco.com/matrix/monitoring/models/eventformat/machineinfomodel">
  &ltmachineinfoeventmodel:JVMInfoEvent contextId="442defcf-8607-4b70-b79a-6b8b5190f5e1" physicalComponentId="/1" freeMemory="296568096" totalMemory="415563776" maxMemory="954466304" nonHeapMemoryInUse="104354984" startTime="1256754183904" uptime="1313426102" threadCount="48" daemonThreadCount="32" peakThreadCount="53" openFileDescriptorCount="48" maxFileDescriptorCount="8192" committedVirtualMemorySize="1760862208" freePhysicalMemorySize="394899456" freeSwapSpaceSize="1040523264" processCpuTime="1745570000000" totalPhysicalMemorySize="3166253056" totalSwapSpaceSize="2155012096"/>
  &ltbase:MatrixPhysicalECompId field1="BEBSPMTest" field2="devjclvamx305" field3="BEBSPMTest_devjclvamx405_nod1" field4="Linux"/>
</xmi:XMI>
'}
}}}
3. Check the value of field3 which is node name, and fields. Find the unwanted node. Shut it down.
4. If can not find such node, purge the queue activematrix.stats.&ltAMX_CLUSTER_NAME>.

What does it mean of "rules.metricspublisher.AMSGRuleFunctions ERROR - Error publishing node JVM info to db java.lang.NullPointerException" and how to troubleshooting it.