correctly check if variable contains nothing... sh-style
correctly check if variable contains nothing... sh-style

meyerj/catkin,thaddeustaylor/catkin,harmishhk/catkin,meyerj/catkin,thaddeustaylor/catkin,jack-oquin/catkin,shyamalschandra/catkin,meyerj/catkin,scpeters/catkin,thaddeustaylor/catkin,shyamalschandra/catkin,scpeters/catkin,beni55/catkin,harmishhk/catkin,jack-oquin/catkin,harmishhk/catkin,asmodehn/catkin,beni55/catkin,wkentaro/catkin,ros/catkin,scpeters/catkin,wkentaro/catkin,jack-oquin/catkin,beni55/catkin,ros/catkin,asmodehn/catkin,shyamalschandra/catkin,wkentaro/catkin,ros/catkin,asmodehn/catkin