https://github.com/PedroLucena-creator/Source-Code-Inspection/blob/56b0f5f298c765bf108a41a45cc744f46a5bd433/Source%20Code%20Inspection/src/br/calebe/ticketmachine/core/TicketMachine.java#L40 O troco precisa ser retornado. Não deve ser null.
https://github.com/PedroLucena-creator/Source-Code-Inspection/blob/56b0f5f298c765bf108a41a45cc744f46a5bd433/Source%20Code%20Inspection/src/br/calebe/ticketmachine/core/TicketMachine.java#L40
O troco precisa ser retornado. Não deve ser null.