Hi, I ran into the same issue yesterday on stretch. On a new server installation (no desktop) the package 'time' providing '/usr/bin/time' is not installed by default. Instead the shell keyword 'time' results in an empty string in "time_bin=`which time`".
A dependency on the package 'time' providing '/usr/bin/time' should solve the issue (and installtion of 'time' fixed the issue for me.) Thanks and best regards, Andi