stuck on the "" | {} fromJSON instance

app/Main.hs

@@ -12,8 +12,9 @@ main = do
   manager' <- newManager tlsManagerSettings
   res <- runClientM
     (search
+     (Just 1)
      (Just JSON)
-     (Just "colza")
+     (Just "poison")
      (Nothing))
     (mkClientEnv manager' $ BaseUrl Https "api.isidore.science" 443 "resource")
   case res of

package.yaml

@@ -21,6 +21,7 @@ description:         Please see the README on GitHub at <https://github.com/gith
 
 dependencies:
 - base >= 4.7 && < 5
+- aeson
 - servant
 - servant-client
 - text

src/ISIDORE/Client.hs

@@ -11,8 +11,56 @@ import Servant.Client
 
 import Data.Proxy(Proxy(..))
 import Data.ByteString.Lazy (ByteString)
+import Data.Aeson
 import qualified Data.Text as T
 
+data LocalContent = LocalContent
+  {
+    _lang :: T.Text,
+    _content :: T.Text
+  }
+  deriving (Show)
+
+instance FromJSON LocalContent where
+  parseJSON (Object o) = LocalContent <$>
+                         (o .: "@xml:lang")
+                         <*> (o .: "$")
+
+data Author = Author
+  {
+    _firstName :: T.Text,
+    _lastName :: T.Text
+  }
+  deriving (Show)
+
+instance FromJSON Author where
+  parseJSON (Object o) = Author <$>
+                         (o .: "firstName")
+                         <*> (o .: "lastName")
+
+data MayBeLocal = Local LocalContent | NonLocal T.Text
+  deriving (Show)
+
+
+data IsidoreDoc = IsidoreDoc
+  {
+    _title :: MayBeLocal,
+    _abstract :: MayBeLocal,
+    _authors :: [Author]
+  }
+  deriving (Show)
+
+instance FromJSON IsidoreDoc where
+  parseJSON (Object o) = IsidoreDoc <$>
+                         (responseReplies >>= (.: "title") )
+                         <*> (responseReplies >>= (.: "abstract"))
+                         <*> (responseReplies >>= (.: "enrichedCreators") >>= (.: "creator"))
+    where responseReplies = (o .: "response")
+            >>= (.: "replies")
+            >>= (.: "content")
+            >>= (.: "reply")
+            >>= (.: "isidore")
+
 data Output = JSON
 
 instance ToHttpApiData Output where
@@ -22,6 +70,7 @@ type ISIDOREAPI = Search
 
 -- search?q=colza&output=json&replies=1&author=jm&
 type Search = "search"
+  :> QueryParam "replies" Int
   :> QueryParam "output" Output
   :> QueryParam "q" T.Text
   :> QueryParam "author" T.Text
@@ -30,6 +79,6 @@ type Search = "search"
 isidoreAPI :: Proxy ISIDOREAPI
 isidoreAPI = Proxy
 
-search :: Maybe Output -> Maybe T.Text -> Maybe T.Text -> ClientM T.Text
+search :: Maybe Int -> Maybe Output -> Maybe T.Text -> Maybe T.Text -> ClientM T.Text
 
 search = client isidoreAPI