Can anybody let me know, why this exception throws many times "Error invoking work item filter issues"

Below is the stack trace for this error : I have replaced the confidential information with "xxxx". I am seeing this error exception more often, but unknown of the reason for this. Please help me to fix this issue, which will be really helpful.

2015-03-23 17:04:59,095 [WebContainer : 44 @@ 17:04 xxxxxxxxx /xxxx/com.ibm.team.workitem.common.internal.rest.IWorkItemR
estService/workItem2] ERROR com.ibm.team.workitem.common                        - Error invoking work item filter 'com.ibm.team.workitem.valueproviders.CONDITION._BRfegE_bEeSd
T5JnKlreEg'
com.ibm.team.repository.common.TeamRepositoryException: Unexpected exception type
        at com.ibm.team.workitem.shared.common.internal.valueProviders.ScriptAttributeValueProvider.handleException(ScriptAttributeValueProvider.java:281)
        at com.ibm.team.workitem.shared.common.internal.valueProviders.ScriptAttributeValueProvider.matches(ScriptAttributeValueProvider.java:161)
        at com.ibm.team.workitem.common.internal.attributeValueProviders.AttributeValueProviderRegistry$SafeWorkItemFilter.matches(AttributeValueProviderRegistry.java:132)
        at com.ibm.team.workitem.common.internal.ReadOnlyAttributesByConditionAdvisor.getReadOnlyAttributes(ReadOnlyAttributesByConditionAdvisor.java:95)
        at com.ibm.team.workitem.common.internal.ReadOnlyAttributesByConditionAdvisor.run(ReadOnlyAttributesByConditionAdvisor.java:72)
        at com.ibm.team.process.internal.common.advice.runtime.OperationAdviceManager.runAdvisor(OperationAdviceManager.java:1254)
        at com.ibm.team.process.internal.common.advice.runtime.OperationAdviceManager.runAdvisors(OperationAdviceManager.java:913)
        at com.ibm.team.process.internal.common.advice.runtime.OperationAdviceManager.advise(OperationAdviceManager.java:293)
        at com.ibm.team.process.internal.common.util.AbstractProcess.doAdvise(AbstractProcess.java:197)
        at com.ibm.team.process.internal.service.ServerProcess.access$2(ServerProcess.java:1)
        at com.ibm.team.process.internal.service.ServerProcess$2.run(ServerProcess.java:156)
        at com.ibm.team.repository.service.internal.PrimitiveTransactionService$3.run(PrimitiveTransactionService.java:176)
        at com.ibm.team.repository.service.internal.rdb.RepositoryDatabase.runTransaction(RepositoryDatabase.java:348)
        at com.ibm.team.repository.service.internal.rdb.RepositoryDatabase.runInTransaction(RepositoryDatabase.java:272)
        at com.ibm.team.repository.service.internal.PrimitiveTransactionService.runInTransaction(PrimitiveTransactionService.java:110)
        at com.ibm.team.repository.service.internal.PrimitiveTransactionService.runInTransaction(PrimitiveTransactionService.java:105)
        at sun.reflect.GeneratedMethodAccessor247.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:37)
        at java.lang.reflect.Method.invoke(Method.java:611)
        at org.eclipse.soda.sat.core.internal.record.ExportProxyServiceRecord.invoke(ExportProxyServiceRecord.java:361)
        at org.eclipse.soda.sat.core.internal.record.ExportProxyServiceRecord.access$0(ExportProxyServiceRecord.java:347)
        at org.eclipse.soda.sat.core.internal.record.ExportProxyServiceRecord$ExportedServiceInvocationHandler.invoke(ExportProxyServiceRecord.java:56)
        at $Proxy118.runInTransaction(Unknown Source)
        at com.ibm.team.repository.service.internal.TransactionService.runInTransaction(TransactionService.java:37)
        at sun.reflect.GeneratedMethodAccessor246.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:37)
        at java.lang.reflect.Method.invoke(Method.java:611)
        at org.eclipse.soda.sat.core.internal.record.ExportProxyServiceRecord.invoke(ExportProxyServiceRecord.java:361)
        at org.eclipse.soda.sat.core.internal.record.ExportProxyServiceRecord.access$0(ExportProxyServiceRecord.java:347)
        at org.eclipse.soda.sat.core.internal.record.ExportProxyServiceRecord$ExportedServiceInvocationHandler.invoke(ExportProxyServiceRecord.java:56)
        at $Proxy198.runInTransaction(Unknown Source)
        at com.ibm.team.process.internal.service.ProcessService.runInTransaction(ProcessService.java:4695)
        at com.ibm.team.process.internal.service.ProcessService.runInTransaction(ProcessService.java:4702)
        at com.ibm.team.process.internal.service.ServerProcess.adviseAndExecute(ServerProcess.java:153)
        at com.ibm.team.workitem.service.internal.AuditableServerProcess.adviseAndExecute(AuditableServerProcess.java:86)
        at com.ibm.team.workitem.service.internal.WorkItemRepositoryService.processSave(WorkItemRepositoryService.java:571)
        at com.ibm.team.workitem.service.internal.WorkItemRepositoryService.save(WorkItemRepositoryService.java:494)
at com.ibm.ws.tcp.channel.impl.AioReadCompletionListener.futureCompleted(AioReadCompletionListener.java:165)
        at com.ibm.io.async.AbstractAsyncFuture.invokeCallback(AbstractAsyncFuture.java:217)
        at com.ibm.io.async.AsyncChannelFuture.fireCompletionActions(AsyncChannelFuture.java:161)
        at com.ibm.io.async.AsyncFuture.completed(AsyncFuture.java:138)
        at com.ibm.io.async.ResultHandler.complete(ResultHandler.java:204)
        at com.ibm.io.async.ResultHandler.runEventProcessingLoop(ResultHandler.java:775)
        at com.ibm.io.async.ResultHandler$2.run(ResultHandler.java:905)
        at com.ibm.ws.util.ThreadPool$Worker.run(ThreadPool.java:1646)
Caused by: java.lang.NullPointerException
        at $Proxy2360.matches(Unknown Source)
        at com.ibm.team.workitem.shared.common.internal.valueProviders.ScriptAttributeValueProvider.matches(ScriptAttributeValueProvider.java:159)
        ... 127 more