Of course the file could technically come into existance between L138 and L139. Here's sbt's implementation:

```scala
	/** Moves the contents of `a` to the location specified by `b`.
	* This method deletes any content already at `b` and creates any parent directories of `b` if they do not exist.
	* It will first try `File.renameTo` and if that fails, resort to copying and then deleting the original file.
	* In either case, the original File will not exist on successful completion of this method.*/
	def move(a: File, b: File): Unit =
	{
		if(b.exists)
			delete(b)
		createDirectory(b.getParentFile)
		if(!a.renameTo(b))
		{
			copyFile(a, b, true)
			delete(a)
		}
	}
```