Update ErrorCollector.addError() to check for null
Update ErrorCollector.addError() to check for null

kcooney/junit,junit-team/junit,ashleyfrieze/junit,kcooney/junit,panchenko/junit,alb-i986/junit,mekwin87/junit4,panchenko/junit,stefanbirkner/junit,powazny/junit4,junit-team/junit4,mekwin87/junit4,junit-team/junit4,ashleyfrieze/junit,alb-i986/junit,powazny/junit4,mekwin87/junit4,ashleyfrieze/junit,junit-team/junit,stefanbirkner/junit,junit-team/junit4,junit-team/junit,powazny/junit4,mekwin87/junit4,kcooney/junit,panchenko/junit,stefanbirkner/junit,alb-i986/junit