Fix bug in `format_value` causing warning for NAs #358

All 37 tests pass in 7s

1 files ±0 4 suites ±0 7s ⏱️ ±0s
37 tests ±0 37 ✅ +1 0 💤 ±0 0 ❌ ±0
251 runs ±0 251 ✅ +2 0 💤 ±0 0 ❌ - 1

Results for commit 32f1d9f. ± Comparison against earlier commit d659c36.