If no year is listed in APA style for an citation what should be listed?

From The OWL at Purdue (see related link; use n.d. for no date):

Unknown Author and Unknown Date: If no author or date is given, use the title in your signal phrase or the first Word or two of the title in the parentheses and use the abbreviation "n.d." (for "no date").Another study of students and research decisions discovered that students succeeded with tutoring ("Tutoring and APA," n.d.).