Improve ArrayMergeBuilder

[Tigrov]

Q	A
Is bugfix?	✔️/❌
New feature?	❌
Breaks BC?	❌
Fixed issues

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.40%. Comparing base (f2d31b3) to head (5a772ba).

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #431      +/-   ##
============================================
- Coverage     98.67%   98.40%   -0.27%     
  Complexity      248      248              
============================================
  Files            24       24              
  Lines           753      752       -1     
============================================
- Hits            743      740       -3     
- Misses           10       12       +2     

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