When no UUID has been specified, query-uuid returns

    {"UUID": "00000000-0000-0000-0000-000000000000"}

The doc comment calls this "a null UUID", which I find less than
clear.  RFC 9562 calls it "the nil UUID (all zeroes)", so use that
instead.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240711112228.2140606-4-armbru@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
[Wording improved, commit message adjusted]
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 qapi/machine.json | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/qapi/machine.json b/qapi/machine.json
index 50ff102d56..eb2fd01e95 100644
--- a/qapi/machine.json
+++ b/qapi/machine.json
@@ -305,9 +305,8 @@
 #
 # Since: 0.14
 #
-# .. note:: If no UUID was specified for the guest, a null UUID is
-#    returned.
-#
+# .. note:: If no UUID was specified for the guest, the nil UUID (all
+#    zeroes) is returned.
 ##
 { 'struct': 'UuidInfo', 'data': {'UUID': 'str'} }
 
-- 
2.45.0