code: public Transparency setTransparency(Boolean transparent) {
  		Transparency prop = null;
  		if (transparent != null) {
  			prop = transparent ? Transparency.transparent() : Transparency.opaque();
  		}
  		setTransparency(prop);
  		return prop;
  	}
docs: Sets whether an event is visible to free/busy time searches.
  @param transparent true to hide the event, false to make it visible it,
  or null to remove the property
  @return the property that was created
  @see <a href="http://tools.ietf.org/html/rfc5545#page-101">RFC 5545
  p.101-2</a>
  @see <a href="http://tools.ietf.org/html/rfc2445#page-96">RFC 2445
  p.96-7</a>
  @see <a href="http://www.imc.org/pdi/vcal-10.doc">vCal 1.0 p.36-7</a>