iPhone（iOS）：将文件从主包复制到文档文件夹错误

I am trying to copy some files across from my app bundle to the documents directory on first launch. I have the checks in place for first launch, but they're not included in code snippet for clarity. The problem is that I am copying to the documents directory (which already exists) and in the documentation, it states that: I am trying to copy some files across from my a