Export resolver exceptions

src/Language/GraphQL/Resolver.hs

@@ -6,13 +6,14 @@
 
 -- | Helper functions and exceptions to write resolvers.
 module Language.GraphQL.Resolver
-    ( argument
+    ( ServerException(..)
+    , argument
     , defaultResolver
     ) where
 
 import Control.Monad.Catch (Exception(..), MonadCatch(..), MonadThrow(..))
 import Control.Monad.Trans.Reader (ReaderT, asks)
-import Data.HashMap.Strict ((!))
+import qualified Data.HashMap.Strict as HashMap
 import Data.Text (Text)
 import qualified Data.Text as Text
 import Data.Typeable (cast)
@@ -49,7 +50,8 @@ defaultResolver :: MonadCatch m => Name -> Type.Resolve m
 defaultResolver fieldName = do
     values' <- asks Type.values
     case values' of
-        Type.Object objectValue -> pure $ objectValue ! fieldName
+        Type.Object objectValue
+            | Just result <- HashMap.lookup fieldName objectValue -> pure result
         _nonObject -> throwM $ FieldNotResolvedException fieldName
 
 -- | Takes an argument name, validates that the argument exists, and optionally