Number of pending tasks of a user


I'm trying to create a process where a user can specify a number of pending task and days so he receives a notification after that number of days while he has X number of tasks.

For that I'm trying to get the number of pending tasks of the user with getNumberOfPendingHumanTaskInstances(userID) where userID is the ID of the user. I'm trying to save the resulting long in a Process Variable but it's throwing this error and I'm not sure what's up: