assets\scripts\executeevents.cs(236,24): error cs0122: 'objectpool<t>' is inaccessible due to its protection level code example

Example: assets\scripts\executeevents.cs(236,24): error cs0122: 'objectpool' is inaccessible due to its protection level

public static ObjectPool<List<IEventSystemHandler>> s_HandlerListPool = new ObjectPool<List<IEventSystemHandler>>(null, l => l.Clear());