Initialise empty exceptions array to fix unshift undefined error

[ghost]

Issue #, if available:

448

Description of changes:

Fixes unshift undefined error which can occur when two identical errors are sent consecutively.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.73%. Comparing base (0124e92) to head (c465e93).
Report is 149 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #508      +/-   ##
==========================================
+ Coverage   82.50%   82.73%   +0.22%     
==========================================
  Files          36       36              
  Lines        1743     1743              
==========================================
+ Hits         1438     1442       +4     
+ Misses        305      301       -4     

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[carolabadeer]

Looks good to me!

[ghost]

@carolabadeer thank you for the review and merge.