Lost landing page after upgrade 2.0

Lost existing land page content after upgrade 2.0. Page URL gives a 500 Internal Server Error and when edit the landing page, content has been lost.

Answered in https://github.com/mautic/mautic/issues/1983

When trying to edit the landing page gives the following error:
[2016-07-11 00:09:35] mautic.WARNING: PHP Warning: include(/home/ascmico/public_html/mautic/vendor/twig/twig/lib/Twig/Node/Expression/Test/Defined.php): failed to open stream: No such file or directory - in file /home/ascmico/public_html/mautic/vendor/composer/ClassLoader.php - at line 412 [] []
[2016-07-11 00:09:36] mautic.CRITICAL: Uncaught PHP Exception SymfonyComponentDebugExceptionClassNotFoundException: “Attempted to load class “Twig_Node_Expression_Test_Defined” from the global namespace. Did you forget a “use” statement?” at /home/ascmico/public_html/mautic/app/cache/prod/classes.php line 6705 {“exception”:"[object] (Symfony\Component\Debug\Exception\ClassNotFoundException(code: 0): Attempted to load class “Twig_Node_Expression_Test_Defined” from the global namespace.nDid you forget a “use” statement? at /home/ascmico/public_html/mautic/app/cache/prod/classes.php:6705)"} []
[2016-07-11 00:09:36] mautic.ERROR: Error: Class ‘Twig_Node_Expression_Test_Defined’ not found - in file /home/ascmico/public_html/mautic/app/cache/prod/classes.php - at line 6705 [] []

Lost existing land page content after upgrade 2.0. Page URL gives a 500 Internal Server Error and when edit the landing page, content has been lost.