an optional property is giving an error when undefined (sealed, covariant object)

[gajus]

type RequestResponseType = {|
  
|};

type ResponseType = {|
  +encoding?: string
|};

const request = (): RequestResponseType => {
  return {};
};

const respond = (response: ResponseType) => {};

respond(request());

10:   return {};
             ^ object literal. Inexact type is incompatible with exact type
9: const request = (): RequestResponseType => {
                       ^ exact type: object type
13: const respond = (response: ResponseType) => {};
                               ^ property `encoding`. Property not found in
15: respond(request());
            ^ object type

https://goo.gl/iKKzI6

[gabelevi]

@samwgoldman - this is another report of that thing I asked you about last week. Special casing the empty object bites us once again! I wonder if there's some way for us to seal the empty object when it's obviously not being modified.

@gajus - A possible workaround is return {encoding: undefined};

[vkurchatkin]

Duplicate of #2977