TaskService - Unable to update priority

Hi,

I trying to update task priority with given code. But it's throwing below exception. 

It works fine if I changed from UpdatePriorityType.UPDATE to UpdatePriorityType.INCREMENT, but only it increments the priority rather than setting it to 99.

I have to update to a specific priority (99).

Any help is appreciated. Thank you!

PriorityIdsListType listType = new PriorityIdsListType();

listType.setUpdateType(UpdatePriorityType.UPDATE);

listType.setWorkflowContext(wfct);

listType.setPriority(99);

listType.getTaskId().addAll(taskIds);

taskService.updatePriorityOfTasks(listType);

Error

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com.oracle.xmlns.bpel.workflow.taskservice.WorkflowErrorMessage: 

at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)

at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)