Null Pointer Exception in copying files from remote [duplicate]

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• What is a NullPointerException, and how do I fix it? 12 answers

This question is related to the following answer posted by Zon.

Transfer folder and subfolders using channelsftp in JSch?

I used the following code to copy a folder from remote to local.

public void downloadDir(String sourcePath, String destPath) throws SftpException { // With subfolders and all files.
    // Create local folders if absent.
    try {
        new File(destPath).mkdirs();
    } catch (Exception e) {
        System.out.println("Error at : " + destPath);
    }
    sftpChannel.lcd(destPath);

    // Copy remote folders one by one.
    lsFolderCopy(sourcePath, destPath); // Separated because loops itself inside for subfolders.
}

private void lsFolderCopy(String sourcePath, String destPath) throws SftpException { // List source (remote, sftp) directory and create a local copy of it - method for every single directory.
    Vector<ChannelSftp.LsEntry> list = sftpChannel.ls(sourcePath); // List source directory structure.
    for (ChannelSftp.LsEntry oListItem : list) { // Iterate objects in the list to get file/folder names.
        if (!oListItem.getAttrs().isDir()) { // If it is a file (not a directory).
            if (!(new File(destPath + "/" + oListItem.getFilename())).exists() || (oListItem.getAttrs().getMTime() > Long.valueOf(new File(destPath + "/" + oListItem.getFilename()).lastModified() / (long) 1000).intValue())) { // Download only if changed later.
                new File(destPath + "/" + oListItem.getFilename());
                sftpChannel.get(sourcePath + "/" + oListItem.getFilename(), destPath + "/" + oListItem.getFilename()); // Grab file from source ([source filename], [destination filename]).
            }
        } else if (!".".equals(oListItem.getFilename() || "..".equals(oListItem.getFilename())) {
            new File(destPath + "/" + oListItem.getFilename()).mkdirs(); // Empty folder copy.
            lsFolderCopy(sourcePath + "/" + oListItem.getFilename(), destPath + "/" + oListItem.getFilename()); // Enter found folder on server to read its contents and create locally.
        }
    }
}

But I am getting a null pointer exception at the following line which I am unable to resolve.

Vector<ChannelSftp.LsEntry> list = sftpChannel.ls(sourcePath); // List source directory structure

I get that it has problem reading the source path but why? Please suggest.