Add nil check in ErrorResponse.Error method

[rajatjindal]

fixes #2970

[codecov]

Codecov Report

Merging #2971 (ec14d72) into master (eea6e0a) will decrease coverage by 0.01%.
The diff coverage is 88.88%.

❗ Current head ec14d72 differs from pull request most recent head caea042. Consider uploading reports for the commit caea042 to get more accurate results

@@            Coverage Diff             @@
##           master    #2971      +/-   ##
==========================================
- Coverage   98.11%   98.10%   -0.01%     
==========================================
  Files         149      149              
  Lines       12790    12796       +6     
==========================================
+ Hits        12549    12554       +5     
- Misses        166      167       +1     
  Partials       75       75              

Files	Coverage Δ
github/github.go	97.59% <88.88%> (-0.13%)	⬇️

[gmlewis]

Thank you, @rajatjindal !
LGTM.

Awaiting second LGTM+Approval from any other contributor to this repo before merging.

[gmlewis]

Thank you, @WillAbides !
Merging.