It’s not a bug, in this case. It depends on the behaviour the library is specified to handle, but if you ask me to remove a specific item from a list, and that

It’s not a bug, in this case. It depends on the behaviour the library is specified to handle, but if you ask me to remove a specific item from a list, and that item isn’t in the list, what should I do? I can fail so you can catch it, or if you don’t catch it, you’ll at least see exactly what went wrong. You expected the item to be in the list and it wasn’t. Your preconditions were wrong from the beginning and you have an (unknown) bug in the code. The alternative is that I can’t find the item and I silently suck it up and don’t notify you. If that’s the api we’ve all agreed on, that’s fine. It was on you to check for the thing in the list first and then remove it. But it’s a bit weird if you think about it - now you need to traverse the list twice. Once to check for the existence (and fail out yourself) and once to remove.