Set empty arrays as empty slices

[emmanuelm41]

When decoding a response, slices that has no elements inside are not set as empty slices. This issue makes JSON Marshalling process transform them into nil, instead of []. For context, this is actually required in order to generate canonical JSONs equally on Golang, Rust and JS. The default value on other languages is to convert it to [] instead of nil.

References:

• proposal: encoding/json: "nonil" struct tag to marshal nil slices and maps as non-null golang/go#27589
• JSON marshal empty arrays as "[]" golang/go#31811
• https://stackoverflow.com/questions/41596613/how-to-marshal-an-empty-struct-as-an-empty-array