fix complex default conversion - handle list

[dg-builder]

FieldBuilder19, FieldBuilder110, FieldBuilder111 handle conversion of default values into "acceptable" default values. However, this conversion wasn't handling default values that were non-empty lists.

Added UTs to test this case.

More details on this method in the java doc:

  /**
   * we want to be very generous with what we let users provide for default values.
   * sadly, (modern) avro can only handle specific classes/collections/primitive-wrappers
   * (see org.apache.avro.util.internal.JacksonUtils.toJson(Object, JsonGenerator) in 1.9+)
   * @param mightNotBeFriendly a proposed field default value that might originate from
   *                           a call like AvroCompatibilityHelper.getGenericDefaultValue()
   * @return a representation of the input that avro likes for use as a field default value
   */

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (cd17a70) 45.78% compared to head (0e048de) 45.81%.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #522      +/-   ##
============================================
+ Coverage     45.78%   45.81%   +0.02%     
- Complexity     4444     4445       +1     
============================================
  Files           403      403              
  Lines         28070    28091      +21     
  Branches       4622     4628       +6     
============================================
+ Hits          12853    12871      +18     
+ Misses        13664    13663       -1     
- Partials       1553     1557       +4     

Files	Coverage Δ
...routil1/compatibility/avro110/FieldBuilder110.java	83.33% <100.00%> (+1.51%)	⬆️
...routil1/compatibility/avro111/FieldBuilder111.java	77.38% <100.00%> (+2.05%)	⬆️
...avroutil1/compatibility/avro19/FieldBuilder19.java	83.33% <100.00%> (+1.51%)	⬆️

... and 6 files with indirect coverage changes

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[li-ukumar]

Add an assertEquals test as well

[dg-builder]

The assert isn't the essential part of the test. The essential part is that .build() doesn't fail. Added a comment in the code