code: @ReadOperation
  	public Health healthForComponentInstance(@Selector String component,
  			@Selector String instance) {
  		HealthIndicator indicator = getNestedHealthIndicator(this.healthIndicator,
  				component);
  		HealthIndicator nestedIndicator = getNestedHealthIndicator(indicator, instance);
  		return (nestedIndicator != null) ? nestedIndicator.health() : null;
  	}
docs: Return the {@link Health} of a particular {@code instance} managed by the specified
  {@code component} or {@code null} if that particular component is not a
  {@link CompositeHealthIndicator} or if such instance does not exist.
  @param component the name of a particular {@link CompositeHealthIndicator}
  @param instance the name of an instance managed by that component
  @return the {@link Health} for the component instance of {@code null}