Collection parsing raises an error if the value is nil

[fabioperrella]

Hi! I'm not sure if this is a bug or if there is some way to deal with it.

Given a representable with a collection inside:

class SongRepresenter < Representable::Decorator
  include Representable::JSON  
  
  property :title  
  property :track  
  collection :composers  
end 

When trying to parse a Json with collection: [], it works!

pry(main)> hash = {title: "aa", track: "bb", composers: []}
pry(main)> SongRepresenter.new(Song.new).from_json(hash.to_json)                                                                                                                                                
=> #<Song title="aa", track="bb", composers=[]>

But when setting composer: nil, it raises an error (very difficult to understand):

pry(main)> hash = {title: "aa", track: "bb", composers: nil}
pry(main)> SongRepresenter.new(Song.new).from_json(hash.to_json)                                                                                                                                                
NoMethodError: undefined method `each_with_index' for nil:NilClass
from /home/fabioperrella/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/representable-2.3.0/lib/representable/deserializer.rb:86:in `call'

I tried to use render_nil: true, but the same problem occurred.

I got this problem because Rails 4.x is replacing the [] value by nil -> https://github.com/rails/rails/pull/12251#issuecomment-31032624

Is there any option to a collection accept a nil value?

Is this really a bug?

Thanks!

[fabioperrella]

cc @BCecatto

[maxemitchell]

@fabioperrella just stumbled upon this as I have the same issue, is this actually a bug or did you find an option that gets this to work?

[fabioperrella]

Hey @maxemitchell , sorry, but I'm currently completely out of this context and I can't help you with this

[yogeshjain999]

@maxemitchell Above error is coming while deserializing given json as we can see from the trace, so you can override parsing phase which happens earlier using reader option 🍻

collection :composers, reader: ->(doc, *) { self.composers = Array(doc[:composers])

Note that this error isn't reproducible on latest v3.1.1 (trace shows v2.3.0 is being used)