code: public Object put(String key, Boolean value) {
  		if (value == null) {
  			stateMap.put(key, Type.NULL);
  		} else {
  			stateMap.put(key, Type.BOOLEAN);
  		}
  
  		return super.put(key, value);
  	}
docs: see {@link Map#put(Object, Object)}.
  this method is alternative of {@link #put(String, Object, Type)} call with {@link Type#BOOLEAN}.
  @param key
  @param value
  @return see {@link Map#put(Object, Object)}
  @since 1.4.12
  @author vvakame