JSF error: "WARNING: FacesMessage(s) have been enqueued, but may not have been displayed"

Reason:

I add a msg in FacesContext but I don't have a
in the page to show it. So either don't put a msg in FacesContext (don't show msg) or add a
in the page (show mesg).

page.xhtml:

#{bean.foo()}

Bean.java:

public void foo() {
        //blah blah
            FacesContext.getCurrentInstance().addMessage(null,
                    new FacesMessage(FacesMessage.SEVERITY_INFO,"list was successful",null));
        //blah blah
    }

Output:

com.sun.faces.renderkit.RenderKitUtils renderUnhandledMessages
INFO: WARNING: FacesMessage(s) have been enqueued, but may not have been displayed.
sourceId=null[severity=(INFO 0), summary=(null), detail=(null)]