See also:

• http://stackoverflow.com/questions/34823602/hibernate-jpa-nullpointerexception-when-accessing-singularattribute-parameter
• http://stackoverflow.com/questions/3854687/jpa-hibernate-static-metamodel-attributes-not-populated-nullpointerexception/4892085#4892085
• http://stackoverflow.com/questions/14554945/nullpointerexception-at-org-hibernate-ejb-criteria-path-abstractpathimpl-get
• https://forum.hibernate.org/viewtopic.php?f=1&t=1009869