Cleaning device for an application device

An assembly, comprising:

• a cleaning device for cleaning an application device which, in operation, applies at least one coating agent jet of a coating agent to a component, and
• a jet checking device integrated in the cleaning device in order to check the at least one coating agent jet emitted by the application device, so that the cleaning device forms a structural unit with the jet checking device,
• the jet checking device having an optical sensor for detecting the at least one coating agent jet,
• the jet checking device has a backlight source which emits a light beam onto the optical sensor, the coating agent jet to be checked running in the beam path of the light beam between the backlight source and the optical sensor, so that the optical sensor tests the coating agent jet in the backlight, and
• the jet checking device has a diffuser which is arranged in the beam path of the back light source between the back light source and the coating agent jet to be checked, so that the back light is diffuse.