OpenApi Generator return empty collection instead of null for collection types

[hamidonos]

Situation

Currently the generator will generate methods which will return null for collection types that are @Nullable. This is not very handy since it forces you to create the collection first instead of using it right away.

I think that null collections are not necessary. Absence of value is simply an empty list (which is much safer and easier to work with down the road)

Solution

• Configure the open api generator in a way that it creates empty collections for nullable collection types.
• Remove any unnecessary null checks and collection initializations currently used in other classes