code: public DbxAuthFinish finishFromCode(String code, String redirectUri) throws DbxException {
          return finish(code, redirectUri, null);
      }
docs: Call this after the user has visited the authorizaton URL with a redirectUrl and copy/pasted
  the authorization code that Dropbox gave them.
  
  @param code The authorization code shown to the user when they clicked "Allow" on the
  authorization, page on the Dropbox website, never {@code null}.
  @param redirectUri The original redirect URI used by {@link #authorize}, never {@code null}.
  
  @throws DbxException if an error occurs communicating with Dropbox.