Find the matching IPaymentHandler.
This method should always be tried first before searching for debit and credit payment handlers in isolation with
getDebitPaymentHandler(com.sybase365.mobiliser.money.persistence.model.pi.PaymentInstrument.Type)
and
getCreditPaymentHandler(com.sybase365.mobiliser.money.persistence.model.pi.PaymentInstrument.Type)
the matching payment handler or null if no type can handle both the credit and debit type in one step.