private void throwUnsupportedOperationExceptionIfStandby(final String operationName) {
        if (taskType() == TaskType.STANDBY) {
            throw new UnsupportedOperationException(
                "this should not happen: " + operationName + "() is not supported in standby tasks.");
        }
    }
@throws StreamsException if an attempt is made to access this state store from an unknown node
@throws UnsupportedOperationException if the current streamTask type is standby
streams/src/main/java/org/apache/kafka/streams/processor/internals/ProcessorContextImpl.java