Fixes boolean algebra miss introduces from b886cc2
Fixes boolean algebra miss introduces from b886cc2

unless starttime.nil? && endtime.nil? is not correct. If 'endtime'
is nil, 'starttime.nil? && endtime.nil?' is false, which 'unless'
turns true, which causes the validation to crash!

ehannes/fullcalendar-rails-engine,ehannes/fullcalendar-rails-engine,ehannes/fullcalendar-rails-engine