modified-helper does not notice change in count

[Bruno Meilick]

when caching a collection like $page->children() only existing objects are tracked.

this creates two bugs.

• one when an objects is removed (easy to fix, will do)
• another when an objects was added to the collection (no idea yet)

[Bruno Meilick]

a expire timer could semi-solve the issue with adding objects. cache will then work well for short repeated calls but not longterm. please upvote if you like this.

[Bruno Meilick]

if object in collection was removed the helper will not notice that and return null.

foreach($collection as $p) {
   if($p == null) continue; // avoid crashing like this
   // ... do stuff
}