From 0e22d19800514f14ca838257b2debb809e7ef939 Mon Sep 17 00:00:00 2001
From: Alp Mestanogullari <alpmestan@gmail.com>
Date: Fri, 19 Jun 2015 11:30:44 +0200
Subject: [PATCH] Make Link take a Maybe argument for MatrixParam, just like
 QueryParam

---
 servant/src/Servant/Utils/Links.hs      | 6 +++---
 servant/test/Servant/Utils/LinksSpec.hs | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/servant/src/Servant/Utils/Links.hs b/servant/src/Servant/Utils/Links.hs
index 5fa8bd0b..19fdc019 100644
--- a/servant/src/Servant/Utils/Links.hs
+++ b/servant/src/Servant/Utils/Links.hs
@@ -303,10 +303,10 @@ instance (KnownSymbol sym, HasLink sub)
 -- MatrixParam instances
 instance (KnownSymbol sym, ToText v, HasLink sub)
     => HasLink (MatrixParam sym v :> sub) where
-    type MkLink (MatrixParam sym v :> sub) = v -> MkLink sub
-    toLink _ l v =
+    type MkLink (MatrixParam sym v :> sub) = Maybe v -> MkLink sub
+    toLink _ l mv =
         toLink (Proxy :: Proxy sub) $
-            addMatrixParam (SingleParam k (toText v)) l
+            maybe id (addMatrixParam . SingleParam k . toText) mv l
       where
         k = symbolVal (Proxy :: Proxy sym)
 
diff --git a/servant/test/Servant/Utils/LinksSpec.hs b/servant/test/Servant/Utils/LinksSpec.hs
index b261559e..16f13925 100644
--- a/servant/test/Servant/Utils/LinksSpec.hs
+++ b/servant/test/Servant/Utils/LinksSpec.hs
@@ -67,7 +67,7 @@ spec = describe "Servant.Utils.Links" $ do
                                           :> "child"
                                           :> MatrixParam "gender" String
                                           :> Get '[JSON] String)
-        apiLink l3 ["Hubert?x=;&", "Cumberdale"] "Edward?"
+        apiLink l3 ["Hubert?x=;&", "Cumberdale"] (Just "Edward?")
             `shouldBeURI` "parent;name[]=Hubert%3Fx%3D%3B%26;\
                            \name[]=Cumberdale/child;gender=Edward%3F"