Exception when moving files

Question

I'm assuming that this has to do with my limited knowledge of how the FileVisitor works and parses the directories. What I'm trying to do is to move the contents of a directory into another directory. I'm doing this by implementing FileVisitor<Path> like this:

public class Mover implements FileVisitor<Path> {

    private Path target;
    private Path source;

    public Mover(Path source, Path target) {
        this.target = target;
        this.source = source;
    }

    @Override
    public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
        Path targetDir = target.resolve(source.relativize(dir));
        try {
            Files.move(dir, targetDir);
        } catch (FileAlreadyExistsException e) {
            if(!Files.isDirectory(targetDir)) {
                System.out.println("Throwing e!");
                throw e;                
            }
        }
        return FileVisitResult.CONTINUE;
    }

    @Override
    public FileVisitResult postVisitDirectory(Path file, IOException exc) throws IOException {
        return FileVisitResult.CONTINUE;
    }

    @Override
    public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
        try {
            Files.move(file, target.resolve(source.relativize(file)));                      
    } catch (NoSuchFileException e) {
                //TODO: Figure out why this exception is raised!
                System.out.println("NoSuchFileException");
            }
        return FileVisitResult.CONTINUE;
    }

    @Override
    public FileVisitResult visitFileFailed(Path file, IOException exc) throws IOException {
        return FileVisitResult.CONTINUE;
    }   
}

In turn I use my class Mover like this:

Files.walkFileTree(from, new Mover(from, to));

I don't like that I add from twice when calling walkFileTree, but currently my problem is mainly with the line under the TODO in my code (however I would very much appreciate any comments on how to solve that to). I don't understand why that exception is raised. I'm guessing that it is because the file is already moved. If that is the case how do I go about to stop my code from trying to move it again, is the way I'm doing it now more or less correct?