Provide a fallback if the serialization is broken

[uhafner]

See https://github.com/jenkinsci/code-coverage-api-plugin/issues/647

[codecov]

Codecov Report

Merging #671 (41cdec4) into master (e486bea) will decrease coverage by 0.12%.
The diff coverage is 43.75%.

❗ Current head 41cdec4 differs from pull request most recent head 6677673. Consider uploading reports for the commit 6677673 to get more accurate results

@@             Coverage Diff              @@
##             master     #671      +/-   ##
============================================
- Coverage     73.55%   73.44%   -0.12%     
- Complexity     1663     1665       +2     
============================================
  Files           129      129              
  Lines          6240     6254      +14     
  Branches        668      671       +3     
============================================
+ Hits           4590     4593       +3     
- Misses         1431     1439       +8     
- Partials        219      222       +3     

Impacted Files	Coverage Δ
...ns/coverage/metrics/steps/CoverageBuildAction.java	69.06% <43.75%> (-3.74%)	⬇️

... and 1 file with indirect coverage changes

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