As I am on a few discord servers that focus on helping player coding spigot plugins, we ran into a quite strange issue when it comes to PotionEffectType#values.

The task was to provide a list of all available PotionEffectTypes to a player and the code to achieve that was this: 

Stream.of(PotionEffectType.values()).map(PotionEffectType::getName).forEach(player::sendMessage);

One would expect that this prints a list of the 30 available PotionEffectTypes to the player, yet it causes a NullPointerException. 

/**
 * Returns an array of all the registered {@link PotionEffectType}s.
 * This array is not necessarily in any particular order and may contain null.
 *
 * @return Array of types.
 */
public static PotionEffectType[] values() {
    return byId.clone();
}

As this is the code to provide the array of PotionEffectTypes, it simply clones the array ordered by id. As the first PotionEffectType has the id 1 and is stored on index 1 instead of 0, the final array has a size of 31 values.

The value at index 0 is therefore just null, which I find to be counterintuitive to what you would expect from the method. I would open a PR, but I would like confirmation that this is not intended. 

The java docs state that there may be null values, but I still do not believe a method designed after the Enum#values method should. 

The solution would be to simply use Arrays.copyOfRange(array , a , array.length) on the byID array