Merge pull request #465 from seagreen/doc-change

Make the comment on `.:!` more accurate.

Data/Aeson/Types/FromJSON.hs

@@ -657,9 +657,9 @@ obj .: key = case H.lookup key obj of
                Just v  -> parseJSON v <?> Key key
 {-# INLINE (.:) #-}
 
--- | Retrieve the value associated with the given key of an 'Object'.  The
--- result is 'Nothing' if the key is not present or value is 'Null', or 'empty'
--- if the value cannot be converted to the desired type.
+-- | Retrieve the value associated with the given key of an 'Object'. The
+-- result is 'Nothing' if the key is not present or if its value is 'Null',
+-- or 'empty' if the value cannot be converted to the desired type.
 --
 -- This accessor is most useful if the key and value can be absent
 -- from an object without affecting its validity.  If the key and
@@ -670,8 +670,12 @@ obj .:? key = case H.lookup key obj of
                Just v  -> parseJSON v <?> Key key
 {-# INLINE (.:?) #-}
 
--- | Like '.:?', but the resulting parser will fail,
--- if the key is present but is 'Null'.
+-- | Retrieve the value associated with the given key of an 'Object'.
+-- The result is 'Nothing' if the key is not present or 'empty' if the
+-- value cannot be converted to the desired type.
+--
+-- This differs from '.:?' by attempting to parse 'Null' the same as any
+-- other JSON value, instead of interpreting it as 'Nothing'.
 (.:!) :: (FromJSON a) => Object -> Text -> Parser (Maybe a)
 obj .:! key = case H.lookup key obj of
                Nothing -> pure Nothing