Small tweaks for servant-server

src/Servant/API.hs

@@ -47,7 +47,8 @@ module Servant.API (
 import Servant.API.Alternative ( (:<|>)(..) )
 import Servant.API.Capture ( Capture )
 import Servant.API.ContentTypes ( HTML, XML, JSON, JavaScript, CSS
-                                , PlainText, OctetStream )
+                                , PlainText, OctetStream, MimeRender(..)
+                                , MimeUnrender(..))
 import Servant.API.Delete ( Delete )
 import Servant.API.Get ( Get )
 import Servant.API.Header ( Header )

src/Servant/API/ContentTypes.hs

@@ -110,7 +110,7 @@ instance ( AllMimeRender ctyps a, IsNonEmpty ctyps
 class Accept ctype => MimeUnrender ctype a where
     fromByteString :: Proxy ctype -> ByteString -> Either String a
 
-class AllCTUnrender list a where
+class (IsNonEmpty list) => AllCTUnrender list a where
     handleCTypeH :: Proxy list
                  -> ByteString     -- Content-Type header
                  -> ByteString     -- Request body