What are the grounds for appeal against a finding that a defendant was advised of his right to file a supplemental brief after the date of the filing of the opening brief?

Appointed counsel for defendant Cecil Dupri Deshon Deloney asked this court to review the record to determine whether there are any arguable issues on appeal. (People v. Wende (1979) 25 Cal.3d 436.) Defendant was advised of his right to file a supplemental brief within 30 days of the date of filing of the opening brief. More than 30 days elapsed and we received no communication from defendant. Finding no arguable error that would result in a disposition more favorable to defendant, we affirm.