In com.liferay.portal.spring.transaction.TransactionInterceptor you find the following lines of code
TransactionInfo transactionInfo = createTransactionIfNecessary(
TransactionStatus transactionStatus =
The TransactionInfo object returned by createTransactionIfNecessary is not guaranteed to hold a TransactionStatus object.
This is for instance not the case when you are using a AnnotationTransactionAttributeSource and the object that is being intercepted does not have a @Transactional anywhere
One way to reproduce this is install liferay 6.0.6 apply the fix for
LPS-14475, install kaleo and in the control panel go to "my workflow tasks"