--- loncom/lonnet/perl/lonnet.pm	2020/10/15 18:09:10	1.1428
+++ loncom/lonnet/perl/lonnet.pm	2020/10/15 19:17:40	1.1429
@@ -1,7 +1,7 @@
 # The LearningOnline Network
 # TCP networking package
 #
-# $Id: lonnet.pm,v 1.1428 2020/10/15 18:09:10 raeburn Exp $
+# $Id: lonnet.pm,v 1.1429 2020/10/15 19:17:40 raeburn Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -8767,16 +8767,18 @@ sub get_commblock_resources {
                                         my $first = $mapres->map_start();
                                         my $finish = $mapres->map_finish();
                                         my $it = $navmap->getIterator($first,$finish,undef,0,0);
-                                        my $res;
-                                        while ($res = $it->next(undef,1)) {
-                                            next unless (ref($res));
-                                            my $symb = $res->symb();
-                                            next if (($symb eq $mapsymb) || ($symb eq ''));
-                                            @interval=&EXT("resource.0.interval",$symb);
-                                            if ($interval[1] eq 'map') {
-                                                if ($res->answerable()) {
-                                                    push(@to_test,$res);
-                                                    last;
+                                        if (ref($it)) {
+                                            my $res;
+                                            while ($res = $it->next(undef,1)) {
+                                                next unless (ref($res));
+                                                my $symb = $res->symb();
+                                                next if (($symb eq $mapsymb) || ($symb eq ''));
+                                                @interval=&EXT("resource.0.interval",$symb);
+                                                if ($interval[1] eq 'map') {
+                                                    if ($res->answerable()) {
+                                                        push(@to_test,$res);
+                                                        last;
+                                                    }
                                                 }
                                             }
                                         }