NullPointerException due to null TaskData in BPM Suite

Issue

• I get NullPointerException when I start a Task in BPMS 6.4.3, which database is migrated from BRMS 5.3.1. It seems TaskImpl is loaded but TaskImpl.taskData is null.

java.lang.NullPointerException
        at org.jbpm.services.task.internals.lifecycle.MVELLifeCycleManager.evalCommand(MVELLifeCycleManager.java:113) ~[jbpm-human-task-core-6.5.0.Final-redhat-9.jar:6.5.0.Final-redhat-9]
        at org.jbpm.services.task.internals.lifecycle.MVELLifeCycleManager.taskOperation(MVELLifeCycleManager.java:369) ~[jbpm-human-task-core-6.5.0.Final-redhat-9.jar:6.5.0.Final-redhat-9]
        at org.jbpm.services.task.impl.TaskInstanceServiceImpl.start(TaskInstanceServiceImpl.java:301) ~[jbpm-human-task-core-6.5.0.Final-redhat-9.jar:6.5.0.Final-redhat-9]
        at org.jbpm.services.task.commands.StartTaskCommand.execute(StartTaskCommand.java:49) ~[jbpm-human-task-core-6.5.0.Final-redhat-9.jar:6.5.0.Final-redhat-9]
        at org.jbpm.services.task.commands.StartTaskCommand.execute(StartTaskCommand.java:30) ~[jbpm-human-task-core-6.5.0.Final-redhat-9.jar:6.5.0.Final-redhat-9]
        at org.jbpm.services.task.commands.CompositeCommand.execute(CompositeCommand.java:148) ~[jbpm-human-task-core-6.5.0.Final-redhat-9.jar:6.5.0.Final-redhat-9]
        at org.jbpm.services.task.commands.TaskCommandExecutorImpl$SelfExecutionCommandService.execute(TaskCommandExecutorImpl.java:65) ~[jbpm-human-task-core-6.5.0.Final-redhat-9.jar:6.5.0.Final-redhat-9]
        at org.drools.core.command.impl.AbstractInterceptor.executeNext(AbstractInterceptor.java:41) ~[drools-core-6.5.0.Final-redhat-9.jar:6.5.0.Final-redhat-9]
        at org.jbpm.services.task.persistence.TaskTransactionInterceptor.execute(TaskTransactionInterceptor.java:69) ~[jbpm-human-task-jpa-6.5.0.Final-redhat-9.jar:6.5.0.Final-redhat-9]