Improve converters.

Replace old syntax with new one and improve
implementation.

test/autotest/test_suite/json_book_converter.e

@@ -4,7 +4,8 @@ note
     date: "$Date$"
     revision: "$Revision$"
 
-class JSON_BOOK_CONVERTER
+class
+	JSON_BOOK_CONVERTER
 
 inherit
     JSON_CONVERTER
@@ -31,17 +32,14 @@ feature -- Access
 feature -- Conversion
 
     from_json (j: like to_json): detachable like object
-        local
-            ucs1, ucs2: detachable STRING_32
-            a: detachable AUTHOR
         do
-            ucs1 ?= json.object (j.item (title_key), Void)
-            check ucs1 /= Void end
-            ucs2 ?= json.object (j.item (isbn_key), Void)
-            check ucs2 /= Void end
-            a ?= json.object (j.item (author_key), "AUTHOR")
-            check a /= Void end
-            create Result.make (ucs1, a, ucs2)
+            if
+				attached {STRING_32} json.object (j.item (title_key), Void) as l_title and
+				attached {STRING_32} json.object (j.item (isbn_key), Void) as l_isbn and
+				attached {AUTHOR} json.object (j.item (author_key), "AUTHOR") as l_author
+            then
+				create Result.make (l_title, l_author, l_isbn)
+            end
         end
 
     to_json (o: like object): JSON_OBJECT
@@ -52,19 +50,22 @@ feature -- Conversion
             Result.put (json.value (o.author), author_key)
         end
 
-feature    {NONE} -- Implementation
+feature {NONE} -- Implementation
 
     title_key: JSON_STRING
+			-- Book's title label.
         once
             create Result.make_json ("title")
         end
 
     isbn_key: JSON_STRING
+			-- Book ISBN label.
         once
             create Result.make_json ("isbn")
         end
 
     author_key: JSON_STRING
+			-- Author label.
         once
             create Result.make_json ("author")
         end