Fix: guard against potential nil pointer dereference

psiphon/server/psinet/psinet.go

@@ -161,6 +161,10 @@ func (db *Database) GetHomepages(sponsorID, clientRegion string, isMobilePlatfor
 		}
 	}
 
+	if sponsor == nil {
+		return sponsorHomePages
+	}
+
 	homePages := sponsor.HomePages
 
 	if isMobilePlatform {
@@ -242,6 +246,10 @@ func (db *Database) GetHttpsRequestRegexes(sponsorID string) []map[string]string
 		sponsor, _ = db.Sponsors[db.DefaultSponsorID]
 	}
 
+	if sponsor == nil {
+		return regexes
+	}
+
 	// If neither sponsorID or DefaultSponsorID were found, sponsor will be the
 	// zero value of the map, an empty Sponsor struct.
 	for _, sponsorRegex := range sponsor.HttpsRequestRegexes {