Problem Statement: content apps can also manage list based data. A list of countries for example. This works until the content should be referenced in another app. Then the choose dialog fails to open because it expects the tree view.

Justification: I came across this problem in several situations where developers try to do the next steps with content apps. It is hopefully not hard to fix

Solution: If it is only a configuration issue then the at least the error message should give more information why the call failed.

Original report by Tom
When no "Tree View" is defined in an App's "contentViews", only a "List View" (as often happen in structured data), it ends with a NPE because magnolia always try to load the "Tree View" at first.

When Adding a "Tree View" everything is working, but we do not want a Tree View, since in the Edtior can move Nodes into nodes, which should not be possible.

Stacktrace: https://gist.github.com/p4elkin/d40c12c10c699c851663