qobject: Add a special null QObject

I'm going to fix the JSON parser to recognize null.  The obvious
representation of JSON null as (QObject *)NULL doesn't work, because
the parser already uses it as an error value.  Perhaps we should
change it to free NULL for null, but that's more than I can do right
now.  Create a special null QObject instead.

The existing QDict, QList, and QString all represent something that
is a pointer in C and could therefore be associated with NULL.  But
right now, all three of these sub-types are always non-null once
created, so the new null sentinel object is intentionally unrelated
to them.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/qobject/qjson.c b/qobject/qjson.c
index f2857c13ea..846733dafb 100644
--- a/qobject/qjson.c
+++ b/qobject/qjson.c
@@ -127,6 +127,9 @@ static void to_json_list_iter(QObject *obj, void *opaque)
 static void to_json(const QObject *obj, QString *str, int pretty, int indent)
 {
     switch (qobject_type(obj)) {
+    case QTYPE_QNULL:
+        qstring_append(str, "null");
+        break;
     case QTYPE_QINT: {
         QInt *val = qobject_to_qint(obj);
         char buffer[1024];