Nim empty string initialize benchmarking

bench.nim

import stopwatch

var c1, c2: stopwatch.clock
for a in 1..10:
  bench(c1):
    for i in 0..1_000_000:
      var x = ""
      x = "Vietnam"
      x = ""
      x = "Cong Hoa Xa Hoi Chu Nghia VietNam"
  bench(c2):
    for i in 0..1_000_000:
      var x = newString(0)
      x = "Vietnam"
      x = newString(0)
      x = "Cong Hoa Xa Hoi Chu Nghia VietNam"

  echo "bench 1): ", c1.seconds
  echo "bench 2): ", c2.seconds

output.txt

bench 1): 0.168687648s
bench 2): 0.143442351s
bench 1): 0.154993121s
bench 2): -4.143262152s
bench 1): 0.147635408s
bench 2): 0.169453555s
bench 1): 0.16333341s
bench 2): 0.151618036s
bench 1): 0.150937742s
bench 2): 0.148614152s
bench 1): 0.177947353s
bench 2): 0.161993457s
bench 1): 0.17322778s
bench 2): 0.153794209s
bench 1): 0.151196786s
bench 2): 0.148051352s
bench 1): 0.152092145s
bench 2): 0.155017354s
bench 1): 0.14786121s
bench 2): 0.180426113s