I've attached a prefab to a script, but it still says the variable has not been assigned

Please see this screenshot: Imgur: The magic of the Internet
As you can see, I created an example prefab of a bomb, and attached it to the spawner script from an example project by the use of a new variable and dropping the prefab into the associated space on the inspector panel. However, when I run the script, the error (which can be seen in red on the bottom left) appears, claiming that the variable is unassigned. Any ideas?

Which GameObject has the script SpawnerScript attached?
For example, GameObject A has SpawnerScript attached, then select GameObject A, in the Inspector, there will be something like ‘Bomb Prefab None (Transform)’ in the SpawnerScript component area, you should drag bombPrefab GameObject to this area and the error will be gone.