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https://issues.apache.org/jira/browse/WICKET-808?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12517326
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Eelco Hillenius commented on WICKET-808:
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Yeah, you're right.
Things like this happen when e.g. list view components mutate the model in
onBeforeRender. We had this piece of code which is part of a panel that nests a
listview:
protected void onBeforeRender() {
super.onBeforeRender();
statuses.clear();
statuses.addAll(Ts4Session.get().getStatuses());
Ts4Session.get().clearStatuses();
}
This resulted in a NPE because that super call at the start would result in the
list view building it's children based on the statuses before any of the
operations you see above were applied, while renderIterator is based on the
size of the model.
So a better fix here would be to base the render iterator on the number of
children. Though the disadvantage of that is that the above bug (which can be
fixed by moving the super call to the bottom) would be hard to detect (it would
be silent).
> print out warning instead of letting NPE happen for repeaters when they have
> null elements.
> -------------------------------------------------------------------------------------------
>
> Key: WICKET-808
> URL: https://issues.apache.org/jira/browse/WICKET-808
> Project: Wicket
> Issue Type: Improvement
> Affects Versions: 1.3.0-beta2
> Reporter: Eelco Hillenius
> Assignee: Eelco Hillenius
> Fix For: 1.3.0-beta3
>
>
> Currently, when you provide null elements in the model (renderIterator),
> you'll get a NPE exception further down the line (in ListView#renderItem for
> instance). We should either throw an meaningful exception earlier, or we
> should make repeaters more lenient and just print out a warning message. I
> opt for the latter. This should be clear enough when developing (you probably
> would wonder where your data is to start with) and a lot better than
> unexpectedly getting NPEs in a production systems in case you missed it.
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