Feature/df explicit na factor level method - #1493

    1 files  ±0     85 suites  ±0   1m 40s ⏱️ -6s
  931 tests ±0    922 ✅ ±0    9 💤 ±0  0 ❌ ±0 
2 313 runs  ±0  1 598 ✅ ±0  715 💤 ±0  0 ❌ ±0 

Results for commit b60d27f. ± Comparison against earlier commit 0184463.