Header: Display error message when the session name is empty.

Reported-by: lhnguyenduc & bnurbekov
Signed-off by: Long Nguyen Duc <lhnguyenduc@wpi.edu> and Batyr Nurbekov <bnurbekov@wpi.edu>
Merge pull request #74 from hlong290494/sbl-dev

Display error message when the session name is empty.