fixed crash with online courses

1 job for dev-2.1 in 2 minutes and 15 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
failed #7386
test

00:02:15

 
Name Stage Failure
failed
test Test

Offenses:

app/controllers/schedules_controller.rb:24:18: C: Style/SymbolProc: Pass &:nil? as an argument to reject! instead of a block.
@all.reject! { |s| s.nil? }
^^^^^^^^^^^^^^

97 files inspected, 1 offense detected
ERROR: Job failed: exit code 1