Inconsistent JSON conversion for proto message with repeated field

[hrsht]

If a proto message has a repeated field and that field is an empty array, the JSON serialization of the proto is inconsistent. Here is an example

class SomeArray < ::Protobuf::Message
  repeated :int32, :arr, 1
end

[2] pry(main)> some_arr = SomeArray.new
=> #<SomeArray arr=[]>
[3] pry(main)> some_arr.to_json
=> "{\"arr\":[]}"
[4] pry(main)> some_arr.arr = []
=> []
[5] pry(main)> some_arr.to_json
=> "{}"
[6] pry(main)> some_arr.arr
=> []
[7] pry(main)> some_arr.to_json
=> "{\"arr\":[]}"

This inconsistency is because setting an empty array to the repeated field deletes the key for that field from the internal message hash (named values). While referencing the field sets the default value of the field back in the internal values hash, which is an empty array.

IMO, when setting the field to an empty array, it should not delete the key from the internal values hash. However, I am open to any other suggestions.

Though, irrespective of the solution, the .to_json (and .to_hash) calls should return consistent results.