Return the transaction attribute, given this set of attributes attached to a method or class. Return null if it's not transactional.
The ITransactionAttribute configured transaction attribute, or null if none was found.
Protected rather than private as subclasses may want to customize how this is done: for example, returning a ITransactionAttribute affected by the values of other attributes. This implementation takes into account RollbackRuleAttributes, if the TransactionAttribute is a RuleBasedTransactionAttribute.