handle sum type nullary constructors in generic JSON

src/Gargantext/Utils/Argonaut.purs

@@ -56,6 +56,11 @@ instance genericSumDecodeJsonRepConstructor ::
     argument <- genericSumDecodeJsonRep inner
     pure $ GR.Constructor argument
 
+instance genericSumDecodeJsonRepNoArguments ::
+  GenericSumDecodeJsonRep (GR.NoArguments) where
+  genericSumDecodeJsonRep _ = do
+    pure GR.NoArguments
+
 instance genericSumDecodeJsonRepArgument ::
   ( Argonaut.DecodeJson a
   ) => GenericSumDecodeJsonRep (GR.Argument a) where
@@ -79,6 +84,10 @@ instance genericSumEncodeJsonRepConstructor ::
     let argument = genericSumEncodeJsonRep inner
     Argonaut.jsonSingletonObject name argument
 
+instance genericSumEncodeJsonRepNoArguments ::
+  GenericSumEncodeJsonRep GR.NoArguments where
+  genericSumEncodeJsonRep GR.NoArguments = Argonaut.jsonNull
+
 instance genericSumEncodeJsonRepArgument ::
   ( Argonaut.EncodeJson a
   ) => GenericSumEncodeJsonRep (GR.Argument a) where

test/Gargantext/Utils/Spec.purs

@@ -17,6 +17,7 @@ data Fruit
   = Boat { hi :: Int }
   | Gravy String
   | Pork Int
+  | Chicken
 
 derive instance eqFruit :: Eq Fruit
 derive instance genericFruit :: Generic Fruit _
@@ -76,3 +77,9 @@ spec =
       let result2' = Argonaut.decodeJson result2
       Argonaut.stringify result2 `shouldEqual` """{"Gravy":"hi"}"""
       result2' `shouldEqual` Right input2
+
+      let input3 = Chicken
+      let result3 = Argonaut.encodeJson input3
+      let result3' = Argonaut.decodeJson result3
+      Argonaut.stringify result3 `shouldEqual` """{"Chicken":null}"""
+      result3' `shouldEqual` Right input3