There's certainly a lot that could be said about the gaps in Apple's developer docs, but the answer to that question is literally, "handle your errors instead o

There's certainly a lot that could be said about the gaps in Apple's developer docs, but the answer to that question is literally, "handle your errors instead of ignoring them, and it will tell you what went wrong." They ignored errors, so didn't know there was no "Documents" directory, and their file write therefore failed.