code: private CommandFaceButtonManager getButtonManager(String faceDescriptorId) {
  		if (this.faceButtonManagers == null) {
  			this.faceButtonManagers = new AbstractCachingMapDecorator() {
  				protected Object create(Object key) {
  					return new CommandFaceButtonManager(AbstractCommand.this, (String) key);
  				}
  			};
  		}
  		CommandFaceButtonManager m = (CommandFaceButtonManager) this.faceButtonManagers.get(faceDescriptorId);
  		return m;
  	}
docs: Returns the {@link CommandFaceButtonManager} for the given
  faceDescriptorId.
  
  @param faceDescriptorId id of the {@link CommandFaceDescriptor}.
  @return the {@link CommandFaceButtonManager} managing buttons configured
  with the {@link CommandFaceDescriptor}.