Invalid JSON generated by genericToEncoding

[alexanderkjeldaas]

omitNothingFields does not work for genericToEncoding

> data Test = Test { x :: Maybe String, y :: Maybe String }  deriving (Generic)
> instance ToJSON Test where toEncoding =
      genericToEncoding defaultOptions {omitNothingFields = True}
> encode $ Test Nothing Nothing
"{,}"

[bergmark]

Thank you for the report!

This is similar to #366 but is not fixed by that PR.

[tolysz]

I do not want to say it; but we miss a constructor of VALUE which represents the values we want to omit. (as it is the container which needs to remove the value; not just value to emit nothing).

Without the additional constructor ( https://skillsmatter.com/skillscasts/6587-programming-with-universal-properties ) there is no way to have a function which maps
Null value to 2 states at the same time.

[Tritlo]

I'm having a similar issue where when I use omitNothingFields, I get an empty ,, i.e.

data GraphResponse = GraphResponse { data :: [Value]
                                   , errors :: Maybe [Value]
                                   , info :: Maybe Value
                                   } deriving (Show, Generic, FromJSON)



instance ToJSON GraphResponse where
  toJSON = genericToJSON defaultOptions {omitNothingFields = True}
  toEncoding = genericToEncoding defaultOptions {omitNothingFields = True}

where GraphResponse [] Nothing Nothing results in the JSON {"data":[],,}, i.e. with extra commas.