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Fix: the next button on the thid page is always active
return null for the getNextPage if the page instance is the third page

Fix the validation to be more flexible

Throw exception instead of leaving error prone code behind
Code fragment should not be reached

Fixed bug concerning the updating through observer functionality

Different handling of displaying the next site

Remove uml.property

Refactoring: push the input fields into the concrete implementation

Pass the selected value

Small change

Fixure for asynchronous missbehaviour