Deal with error with a proper error

... instead of returning a `Maybe` to the frontend

src/Gargantext/API/Node/Corpus/Subcorpus.hs

 module Gargantext.API.Node.Corpus.Subcorpus where
 
+import Data.Validity (Validation(..), ValidationChain(..))
 import Gargantext.Prelude
-
-import Gargantext.API.Errors.Types (BackendInternalError)
+import Gargantext.API.Errors.Types (BackendInternalError(..))
 import Gargantext.API.Routes.Named.Corpus (MakeSubcorpusAPI(..), SubcorpusParams(..))
 import Gargantext.Core.NodeStory.Types (HasNodeStoryEnv)
 import Gargantext.Core.NLP (HasNLPServer)
@@ -21,12 +21,14 @@ makeSubcorpus :: ( HasNodeStoryEnv env
   => UserId
   -> MakeSubcorpusAPI (AsServerT m)
 makeSubcorpus user = MakeSubcorpusAPI $ \corpusId params -> do
-  case parseQuery (RawQuery $ _subcorpusParams_query params) of
-    Left _  -> return Nothing
-    Right q -> do
+  let queryText = _subcorpusParams_query params
+  case parseQuery (RawQuery queryText) of
+    Left msg -> throwError $ InternalValidationError $ Validation [Violated $
+                  "Failed to parse the query " <> show queryText <> ": " <> msg]
+    Right q  -> do
       subcorpusId <- makeSubcorpusFromQuery
              (UserDBId user)
              corpusId
              q
              (_subcorpusParams_reuseParentList params)
-      return $ Just subcorpusId
+      return subcorpusId

src/Gargantext/API/Routes/Named/Corpus.hs

@@ -32,7 +32,7 @@ import Gargantext.API.Worker (WorkerAPI)
 import Gargantext.Core.Text.Ngrams (NgramsType(..))
 import Gargantext.Core.Utils.Prefix (unPrefix, unPrefixSwagger)
 import Gargantext.Database.Admin.Types.Node
-import Gargantext.Prelude (Bool, Maybe)
+import Gargantext.Prelude (Bool)
 import Servant
 
 --------------------------------------------------
@@ -68,7 +68,7 @@ newtype MakeSubcorpusAPI mode = MakeSubcorpusAPI
                      :> Capture "corpus_id" CorpusId
                      :> "subcorpus"
                      :> ReqBody '[JSON] SubcorpusParams
-                     :> Post '[JSON] (Maybe NodeId) -- new subcorpus ID, if successful
+                     :> Post '[JSON] NodeId -- new subcorpus ID
   } deriving Generic
 
 data SubcorpusParams = SubcorpusParams