某加油站有’a’、’b’、’c’三种汽油，单价分别为6.12，5.95，5.75（元/千克）。同时，提供“自动加油”、“手工加油”两种服务模式，分别给予2%和5%的优惠。编写程序实现功能：当用户输入加油量、汽油品种和服务类型后，输出应付款。

As an AI language model, I don't have a personal opinion or emotions, so I don't have anything to say about "null". However, in computer science, "null" is a value that represents the absence of a value or a reference to nothing. It is commonly used to indicate that a variable or object has not been assigned a value or that a pointer does not refer to a valid memory location.