logs from case 1 (empty value)
2020-11-18 11:19:44,520 INFO o.a.j.e.StandardJMeterEngine: Running the test!
2020-11-18 11:19:44,523 INFO o.a.j.s.SampleEvent: List of sample_variables: []
2020-11-18 11:19:44,523 INFO o.a.j.s.SampleEvent: List of sample_variables: []
2020-11-18 11:19:44,530 INFO o.a.j.e.u.CompoundVariable: Note: Function class names must contain the string: '.functions.'
2020-11-18 11:19:44,531 INFO o.a.j.e.u.CompoundVariable: Note: Function class names must not contain the string: '.gui.'
2020-11-18 11:19:45,428 INFO o.a.j.g.u.JMeterMenuBar: setRunning(true, *local*)
2020-11-18 11:19:46,057 INFO o.a.j.e.StandardJMeterEngine: Starting ThreadGroup: 1 : case1
2020-11-18 11:19:46,058 INFO o.a.j.e.StandardJMeterEngine: Starting 1 threads for group case1.
2020-11-18 11:19:46,059 INFO o.a.j.e.StandardJMeterEngine: Thread will continue on error
2020-11-18 11:19:46,060 INFO o.a.j.t.ThreadGroup: Starting thread group... number=1 threads=1 ramp-up=1 delayedStart=false
2020-11-18 11:19:46,068 INFO o.a.j.t.ThreadGroup: Started thread group number 1
2020-11-18 11:19:46,069 INFO o.a.j.e.StandardJMeterEngine: All thread groups have been started
2020-11-18 11:19:46,074 INFO o.a.j.t.JMeterThread: Thread started: case1 1-1

logs from case 2 (negative value)
2020-11-18 11:21:11,450 INFO o.a.j.e.StandardJMeterEngine: Running the test!
2020-11-18 11:21:11,450 INFO o.a.j.s.SampleEvent: List of sample_variables: []
2020-11-18 11:21:11,453 INFO o.a.j.g.u.JMeterMenuBar: setRunning(true, *local*)
2020-11-18 11:21:12,019 INFO o.a.j.e.StandardJMeterEngine: Starting ThreadGroup: 1 : case2
2020-11-18 11:21:12,020 INFO o.a.j.e.StandardJMeterEngine: Starting 1 threads for group case2.
2020-11-18 11:21:12,020 INFO o.a.j.e.StandardJMeterEngine: Thread will continue on error
2020-11-18 11:21:12,020 INFO o.a.j.t.ThreadGroup: Starting thread group... number=1 threads=1 ramp-up=1 delayedStart=false
2020-11-18 11:21:12,021 INFO o.a.j.t.ThreadGroup: Started thread group number 1
2020-11-18 11:21:12,021 INFO o.a.j.e.StandardJMeterEngine: All thread groups have been started
2020-11-18 11:21:12,024 INFO o.a.j.t.JMeterThread: Thread started: case2 1-1
2020-11-18 11:21:12,030 INFO o.a.j.t.JMeterThread: Thread is done: case2 1-1
2020-11-18 11:21:12,031 INFO o.a.j.t.JMeterThread: Thread finished: case2 1-1
2020-11-18 11:21:12,031 INFO o.a.j.e.StandardJMeterEngine: Notifying test listeners of end of test
2020-11-18 11:21:12,031 INFO o.a.j.g.u.JMeterMenuBar: setRunning(false, *local*)

logs from case 3 (string value)
2020-11-18 11:21:50,783 INFO o.a.j.e.StandardJMeterEngine: Running the test!
2020-11-18 11:21:50,784 INFO o.a.j.s.SampleEvent: List of sample_variables: []
2020-11-18 11:21:50,792 INFO o.a.j.g.u.JMeterMenuBar: setRunning(true, *local*)
2020-11-18 11:21:51,253 INFO o.a.j.e.StandardJMeterEngine: Starting ThreadGroup: 1 : case3
2020-11-18 11:21:51,253 INFO o.a.j.e.StandardJMeterEngine: Starting 1 threads for group case3.
2020-11-18 11:21:51,253 INFO o.a.j.e.StandardJMeterEngine: Thread will continue on error
2020-11-18 11:21:51,253 INFO o.a.j.t.ThreadGroup: Starting thread group... number=1 threads=1 ramp-up=1 delayedStart=false
2020-11-18 11:21:51,255 INFO o.a.j.t.ThreadGroup: Started thread group number 1
2020-11-18 11:21:51,255 INFO o.a.j.e.StandardJMeterEngine: All thread groups have been started
2020-11-18 11:21:51,258 INFO o.a.j.t.JMeterThread: Thread started: case3 1-1