frontend BUGFIX creating new list instance with keys only

when a list contains only keys, the error message "nothing to create here"
was always displayed, now it is detected that there is actually nothing to
create and editting of the list content is closed automatically as it was
automatically opened.
diff --git a/frontend/config/modifications.service.ts b/frontend/config/modifications.service.ts
index db2fda0..7327ffa 100644
--- a/frontend/config/modifications.service.ts
+++ b/frontend/config/modifications.service.ts
@@ -347,7 +347,9 @@
             newNode['children'] = [];
             /* open creation dialog for nodes inside the created list */
             this.sessionsService.childrenSchemas(activeSession.key, newNode['info']['path'], newNode).then(result => {
-                this.createOpen(result, newNode);
+                if (result && result.length) {
+                    this.createOpen(result, newNode);
+                }
 
                 if (newNode['schemaChildren'].length) {
                     for (let i in newNode['schemaChildren']) {
@@ -362,6 +364,10 @@
                         this.setEdit(activeSession, newKey, true)
                         newNode['children'].push(newKey)
                         newNode['schemaChildren'].splice(i, 1);
+                        if (!newNode['schemaChildren'].length) {
+                            newKey['last'] = true;
+                            this.createClose(newNode, 'success');
+                        }
                     }
                 }
             });