FIX 'host' not found

src/ISTEX/Client.hs

@@ -55,7 +55,7 @@ data Document = Document
   , _document_authors         :: [Author]
   , _document_abstract        :: Maybe T.Text
   , _document_publicationDate :: Maybe Int
-  , _document_sources         :: Source
+  , _document_sources         :: Maybe Source
   } deriving (Show, Generic)
 L.makeLenses ''Document
 
@@ -65,7 +65,7 @@ instance FromJSON Document where
     _document_title    <- o .:? "title"
     _document_authors  <- o .: "author" <|> pure []
     _document_abstract <- o .:? "abstract"
-    _document_sources  <- o .: "host"
+    _document_sources  <- o .:? "host"
     mPubDate           <- o .:? "publicationDate"
     
     pure $ Document { _document_publicationDate = parsePubDate mPubDate, .. }