code: public DbxClientV2 withPathRoot(PathRoot pathRoot) {
          if (pathRoot == null) {
              throw new IllegalArgumentException("'pathRoot' should not be null");
          }
          return new DbxClientV2(_client.withPathRoot(pathRoot));
      }
docs: Returns a new {@link DbxClientV2} that performs requests against Dropbox API
  user endpoints relative to a namespace without including the namespace as
  part of the path variable for every request.
  (<a href="https://www.dropbox.com/developers/reference/namespace-guide#pathrootmodes">https://www.dropbox.com/developers/reference/namespace-guide#pathrootmodes</a>).
  
  <p> This method performs no validation of the namespace ID. </p>
  
  @param pathRoot  the path root for this client, never {@code null}.
  
  @return Dropbox client that issues requests with Dropbox-API-Path-Root header.
  
  @throws IllegalArgumentException  If {@code pathRoot} is {@code null}