What are the grounds for appeal against the judgment of the Court of Appeal for failing to notify the appellant of a supplemental brief?

Appointed counsel for appellant 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.) We sent a letter to appellant, advising him 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 appellant. Finding no arguable error that would result in a disposition more favorable to appellant, we affirm the judgment.