prevent php-warnings, fixes #4823

app/controllers/admin/courseplanning.php

app/controllers/admin/courses.php

app/controllers/blubber.php

app/controllers/course/contentmodules.php

app/controllers/course/forum/index.php

app/controllers/course/statusgroups.php

app/controllers/course/study_areas.php

app/controllers/course/studygroup.php

app/controllers/settings/privacy.php

app/controllers/tour.php

app/views/consultation/admin/cancel_slots.php

app/views/course/forum/index/index.php

app/views/course/timesrooms/editStack.php

app/views/files_dashboard/_search_tr.php

app/views/resources/room_request/decline.php

lib/classes/coursewizardsteps/BasicDataWizardStep.php

lib/models/BlubberThread.php

lib/models/File.php

lib/models/OERHostOERSI.php

lib/models/SeminarCycleDate.php