Don't try to assing rev to nil map

[flimzy]

Follow-up to #624

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.03 ⚠️

Comparison is base (8758986) 92.44% compared to head (382a047) 92.42%.

❗ Current head 382a047 differs from pull request most recent head 56a14c6. Consider uploading reports for the commit 56a14c6 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #625      +/-   ##
==========================================
- Coverage   92.44%   92.42%   -0.03%     
==========================================
  Files          21       21              
  Lines        1297     1293       -4     
==========================================
- Hits         1199     1195       -4     
  Misses         75       75              
  Partials       23       23              

Impacted Files	Coverage Δ
db.go	95.34% <100.00%> (-0.05%)	⬇️

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