[haskell-http-client] relax Aeson constraint to allow Aeson 1 (#12486)

samples/client/petstore/haskell-http-client/lib/OpenAPIPetstore/Core.hs

@@ -23,6 +23,7 @@ Module : OpenAPIPetstore.Core
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TupleSections #-}
 {-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE CPP #-}
 {-# OPTIONS_GHC -fno-warn-name-shadowing -fno-warn-unused-binds -fno-warn-unused-imports #-}
 
 module OpenAPIPetstore.Core where
@@ -428,7 +429,11 @@ _applyAuthMethods req config@(OpenAPIPetstoreConfig {configAuthMethods = as}) =
 -- * Utils
 
 -- | Removes Null fields.  (OpenAPI-Specification 2.0 does not allow Null in JSON)
+#if MIN_VERSION_aeson(2,0,0)
 _omitNulls :: [(A.Key, A.Value)] -> A.Value
+#else
+_omitNulls :: [(Text, A.Value)] -> A.Value
+#endif
 _omitNulls = A.object . P.filter notNull
   where
     notNull (_, A.Null) = False