android java.io.File.fixSlashes(File.java:185)

java.lang.NullPointerException
at java.io.File.fixSlashes(File.java:185)
at java.io.File.<init>(File.java:134)

保存图片的功能代码是：

public static String sharePhoto(Context context,Bitmap bmp) {
    File folder = new File(Environment.getExternalStorageDirectory().getAbsolutePath() + "/Pictures/Folder");
    Boolean success = true;
    String file_path = null;
    if (!folder.exists()) {
        success = folder.mkdir();
    }
    if (success) {
            file_path = folder + "/Img_" + System.currentTimeMillis() / 1000 + ".jpg";
        }
        OutputStream os = null;
        try {
            os = new FiLeoutputStream(file_path);
            bmp.compress(Bitmap.CompressFormat.JPEG,100,os);
        } catch (IOException E) {
           e.printStackTrace();
        }
    } else {
        // Do something else on failure
    }
    Intent mediaScanIntent = new Intent(Intent.ACTION_MEDIA_SCAnnER_SCAN_FILE);
    File f = new File(file_path);
    Uri contentUri = Uri.fromFile(f);
    mediaScanIntent.setData(contentUri);
    context.sendBroadcast(mediaScanIntent);

    return file_path;
}