Warning message when adding a new Plan

Version: master (16.10)
only happens in php7

I got the following message from Mahara when adding a new Pan as an Admin or as a User

[WAR] ab (artefact/plans/new.php:37) Only variables should be assigned by reference

Call stack (most recent first):
log_message("Only variables should be assigned by reference", 8, true, true, "/home/lisadunmire/code/mahara/htdocs/artefact/plan...", 37) at /home/lisadunmire/code/mahara/htdocs/lib/errors.php:513
error(8, "Only variables should be assigned by reference", "/home/lisadunmire/code/mahara/htdocs/artefact/plan...", 37, array(size 63)) at /home/lisadunmire/code/mahara/htdocs/artefact/plans/new.php:37

[WAR] ab (artefact/plans/new.php:39) Only variables should be passed by reference

Call stack (most recent first):
log_message("Only variables should be passed by reference", 8, true, true, "/home/lisadunmire/code/mahara/htdocs/artefact/plan...", 39) at /home/lisadunmire/code/mahara/htdocs/lib/errors.php:513
error(8, "Only variables should be passed by reference", "/home/lisadunmire/code/mahara/htdocs/artefact/plan...", 39, array(size 64)) at /home/lisadunmire/code/mahara/htdocs/artefact/plans/new.php:39