it seems that the value of the two variables

in the header:
static const std::string PERSISTENCE_PROPERTY_NAME;
static const std::string PERSISTENCE_PROPERTYLIST_NAME;

in the cpp-file:
const std::string mitk::PersistenceService::PERSISTENCE_PROPERTY_NAME("PersistenceNode");
const std::string mitk::PersistenceService::PERSISTENCE_PROPERTYLIST_NAME("PersistenceService");

is not always defined when the persistence service is used. This leads to errors.

So commented out the lines of code which use this variables and replaced them by normal strings for the moment.

This needs to be fixed so that PERSISTENCE_PROPERTY_NAME and PERSISTENCE_PROPERTYLIST_NAME are defined at a central place inside the code file.