Remove Null constructor from Block.

[API change]

Closes jgm#91.

src/Text/Pandoc/Arbitrary.hs

@@ -88,7 +88,6 @@ instance Arbitrary Blocks where
                                                    flattenTableFoot ft
           flattenBlock (Figure _ capt blks) = flattenCaption capt <> blks
           flattenBlock (Div _ blks) = blks
-          flattenBlock Null = []
 
           flattenCaption (Caption Nothing body)    = body
           flattenCaption (Caption (Just ils) body) = Para ils : body
@@ -211,7 +210,6 @@ instance Arbitrary Block where
     [Figure attr' capt blks | attr' <- shrinkAttr attr]
   shrink (Div attr blks) = (Div attr <$> shrinkBlockList blks)
                         ++ (flip Div blks <$> shrinkAttr attr)
-  shrink Null = []
 
 arbBlock :: Int -> Gen Block
 arbBlock n = frequency $ [ (10, Plain <$> arbInlines (n-1))

src/Text/Pandoc/Definition.hs

@@ -88,7 +88,7 @@ module Text.Pandoc.Definition ( Pandoc(..)
 
 import Data.Generics (Data, Typeable)
 import Data.Ord (comparing)
-import Data.Aeson hiding (Null)
+import Data.Aeson
 import Data.Aeson.TH (deriveJSON)
 import qualified Data.Aeson.Types as Aeson
 import qualified Data.Map as M
@@ -305,8 +305,6 @@ data Block
     | Figure Attr Caption [Block]
     -- | Generic block container with attributes
     | Div Attr [Block]
-    -- | Nothing
-    | Null
     deriving (Eq, Ord, Read, Show, Typeable, Data, Generic)
 
 -- | Type of quotation marks to use in Quoted inline.

src/Text/Pandoc/Walk.hs

@@ -485,7 +485,6 @@ walkBlockM f (Div attr bs')           = Div attr <$> walkM f bs'
 walkBlockM _ x@CodeBlock {}           = return x
 walkBlockM _ x@RawBlock {}            = return x
 walkBlockM _ HorizontalRule           = return HorizontalRule
-walkBlockM _ Null                     = return Null
 walkBlockM f (Table attr capt as hs bs fs)
   = do capt' <- walkM f capt
        hs' <- walkM f hs
@@ -523,7 +522,6 @@ queryBlock f (Figure _ capt blks)
   = query f capt <>
     query f blks
 queryBlock f (Div _ bs)               = query f bs
-queryBlock _ Null                     = mempty
 
 -- | Helper method to walk to elements nested below @'MetaValue'@ nodes.
 --

test/test-pandoc-types.hs

@@ -149,7 +149,7 @@ t_metainlines = ( MetaInlines [Space, SoftBreak]
                 )
 
 t_metablocks :: (MetaValue, ByteString)
-t_metablocks = ( MetaBlocks [Null,Null], [s|{"t":"MetaBlocks","c":[{"t":"Null"},{"t":"Null"}]}|])
+t_metablocks = ( MetaBlocks [HorizontalRule,HorizontalRule], [s|{"t":"MetaBlocks","c":[{"t":"HorizontalRule"},{"t":"HorizontalRule"}]}|])
 
 t_singlequote :: (QuoteType, ByteString)
 t_singlequote = (SingleQuote, [s|{"t":"SingleQuote"}|])
@@ -464,9 +464,6 @@ t_div = ( Div ("id", ["kls"], [("k1", "v1"), ("k2", "v2")]) [Para [Str "Hello"]]
          , [s|{"t":"Div","c":[["id",["kls"],[["k1","v1"],["k2","v2"]]],[{"t":"Para","c":[{"t":"Str","c":"Hello"}]}]]}|]
          )
 
-t_null :: (Block, ByteString)
-t_null = (Null, [s|{"t":"Null"}|])
-
 -- headers and rows are padded to a consistent number of
 -- cells in order to avoid syntax errors after conversion, see
 -- jgm/pandoc#4059.
@@ -757,7 +754,6 @@ tests =
         , testEncodeDecode "Table" t_table
         , testEncodeDecode "Figure" t_figure
         , testEncodeDecode "Div" t_div
-        , testEncodeDecode "Null" t_null
         ]
       , testGroup "Table"
         [ testEncodeDecode "Row" t_row