docs: @Nonnull
    public DigestAuthServerBuilder addDomain (@Nonnull final ISimpleURL aURL)
    {
      ValueEnforcer.notNull (aURL, "Url");
  
      final String sURL = aURL.getAsStringWithEncodedParameters ();
      // Check for spaces, as all URLs are concatenated with spaces!
      if (sURL.indexOf (' ') >= 0)
        throw new IllegalArgumentException ("URL may not contain spaces: '" + sURL + "'");
      m_aDomains.add (sURL);
      return this;
    }