[PATCH v3] migration: use "" instead of (null) for tls-authz

[Mao Zhongyi <maozhongyi@cmss.chinamobile.com>]

run:
(qemu) info migrate_parameters
announce-initial: 50 ms
...
announce-max: 550 ms
multifd-compression: none
xbzrle-cache-size: 4194304
max-postcopy-bandwidth: 0
 tls-authz: '(null)'

Migration parameter 'tls-authz' is used to provide the QOM ID
of a QAuthZ subclass instance that provides the access control
check, default is NULL. But the empty string is not a valid
object ID, so use "" instead of the default. Although it will
fail when lookup an object with ID "", it is harmless, just
consistent with tls_creds.

As a bonus, this patch also fixed the bad indentation on the
last line and removed 'has_tls_authz' redundant check in
'hmp_info_migrate_parameters'.

Signed-off-by: Mao Zhongyi <maozhongyi@cmss.chinamobile.com>
---
 migration/migration.c | 3 ++-
 monitor/hmp-cmds.c    | 4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/migration/migration.c b/migration/migration.c
index 4b26110d57..c4c9aee15e 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -790,7 +790,8 @@ MigrationParameters *qmp_query_migrate_parameters(Error **errp)
     params->has_tls_hostname = true;
     params->tls_hostname = g_strdup(s->parameters.tls_hostname);
     params->has_tls_authz = true;
-    params->tls_authz = g_strdup(s->parameters.tls_authz);
+    params->tls_authz = g_strdup(s->parameters.tls_authz ?
+                                 s->parameters.tls_authz : "");
     params->has_max_bandwidth = true;
     params->max_bandwidth = s->parameters.max_bandwidth;
     params->has_downtime_limit = true;
diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
index a71de0e60b..dc48e6986c 100644
--- a/monitor/hmp-cmds.c
+++ b/monitor/hmp-cmds.c
@@ -459,9 +459,9 @@ void hmp_info_migrate_parameters(Monitor *mon, const QDict *qdict)
         monitor_printf(mon, "%s: %" PRIu64 "\n",
             MigrationParameter_str(MIGRATION_PARAMETER_MAX_POSTCOPY_BANDWIDTH),
             params->max_postcopy_bandwidth);
-        monitor_printf(mon, " %s: '%s'\n",
+        monitor_printf(mon, "%s: '%s'\n",
             MigrationParameter_str(MIGRATION_PARAMETER_TLS_AUTHZ),
-            params->has_tls_authz ? params->tls_authz : "");
+            params->tls_authz);
     }
 
     qapi_free_MigrationParameters(params);
-- 
2.17.1