Index: openacs-4/packages/file-storage/www/folder-create.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/file-storage/www/folder-create.tcl,v
diff -u -r1.11.2.2 -r1.11.2.3
--- openacs-4/packages/file-storage/www/folder-create.tcl	19 Oct 2021 14:56:59 -0000	1.11.2.2
+++ openacs-4/packages/file-storage/www/folder-create.tcl	19 Oct 2021 15:08:18 -0000	1.11.2.3
@@ -104,6 +104,15 @@
                   -tolower \
                   $folder_name]
 
+    # 'folder_name' itself cannot be null, but the sanitized 'name'
+    # might be, if 'folder_name' is made only of invalid
+    # characters. We complain in such case, as we need some kind of
+    # valid name to be there.
+    if {[string length $name] == 0} {
+        template::form::set_error folder-ae folder_name [_ acs-tcl.lt_name_contains_invalid [list name [_ file-storage.Title]]]
+        break
+    }
+
     # check folder name does not exist already
     if {[content::item::get_id_by_name \
              -name $name -parent_id $parent_id] ne ""} {