fix: exception was thrown when 0 commits found

[bcoe]

Noticed this in logs when we were testing the new nightly cron.

[codecov]

Codecov Report

Merging #484 into master will decrease coverage by 0.38%.
The diff coverage is 14.81%.

@@            Coverage Diff             @@
##           master     #484      +/-   ##
==========================================
- Coverage   81.64%   81.26%   -0.39%     
==========================================
  Files          41       41              
  Lines        4713     4740      +27     
  Branches      386      363      -23     
==========================================
+ Hits         3848     3852       +4     
- Misses        864      887      +23     
  Partials        1        1              

Impacted Files	Coverage Δ
src/releasers/java-auth-yoshi.ts	23.52% <0.00%> (-1.48%)	⬇️
src/releasers/java-bom.ts	93.89% <22.22%> (-2.55%)	⬇️
src/releasers/java-yoshi.ts	87.98% <22.22%> (-2.17%)	⬇️

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