There are other important lights on the motorcycle, besides the front and rear light. Think of your parking light, indicators and cockpit lighting. Due to wear and vibrations they may give up the ghost over time. As a rule this is at an unexpected and inconvenient moment, and it is wise to always carry a set of spare bulbs. And it's true that a dead 'neutral' bulb is not a disaster, but you don't want to ride without your indicators at night.
There are many different types of bulbs. The easiest way to find the correct replacement is to take the defective one from its housing. Most bulbs have their type designation printed on the lamp fitting, as shown in the picture.
If the type number is not visible, you can compare the socket with the drawing below and determine the type of the lamp that way.
And remember, being able to avoid the fine is nice, but fixing your light is first and foremost for your own safety.