From 79a603758d3b46fa05a4588f0ca19648fa3601d6 Mon Sep 17 00:00:00 2001
From: Yu Watanabe <watanabe.yu+github@gmail.com>
Date: Fri, 11 May 2018 01:22:49 +0900
Subject: [PATCH] core: send NULL instead of empty string

---
 src/core/dbus-execute.c | 2 +-
 src/core/dbus-manager.c | 2 +-
 src/core/dbus-unit.c    | 8 +++-----
 3 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/src/core/dbus-execute.c b/src/core/dbus-execute.c
index 23b98027d3..ff2dfa59d3 100644
--- a/src/core/dbus-execute.c
+++ b/src/core/dbus-execute.c
@@ -312,7 +312,7 @@ static int property_get_empty_string(
         assert(bus);
         assert(reply);
 
-        return sd_bus_message_append(reply, "s", "");
+        return sd_bus_message_append(reply, "s", NULL);
 }
 
 static int property_get_syscall_filter(
diff --git a/src/core/dbus-manager.c b/src/core/dbus-manager.c
index de6aaba229..ced5d06bd4 100644
--- a/src/core/dbus-manager.c
+++ b/src/core/dbus-manager.c
@@ -99,7 +99,7 @@ static int property_get_virtualization(
 
         return sd_bus_message_append(
                         reply, "s",
-                        v == VIRTUALIZATION_NONE ? "" : virtualization_to_string(v));
+                        v == VIRTUALIZATION_NONE ? NULL : virtualization_to_string(v));
 }
 
 static int property_get_architecture(
diff --git a/src/core/dbus-unit.c b/src/core/dbus-unit.c
index 4d168b240d..f93893c62f 100644
--- a/src/core/dbus-unit.c
+++ b/src/core/dbus-unit.c
@@ -81,7 +81,7 @@ static int property_get_following(
         assert(u);
 
         f = unit_following(u);
-        return sd_bus_message_append(reply, "s", f ? f->id : "");
+        return sd_bus_message_append(reply, "s", f ? f->id : NULL);
 }
 
 static int property_get_dependencies(
@@ -235,7 +235,7 @@ static int property_get_unit_file_preset(
         r = unit_get_unit_file_preset(u);
 
         return sd_bus_message_append(reply, "s",
-                                     r < 0 ? "":
+                                     r < 0 ? NULL:
                                      r > 0 ? "enabled" : "disabled");
 }
 
@@ -918,7 +918,7 @@ static int property_get_cgroup(
                 sd_bus_error *error) {
 
         Unit *u = userdata;
-        const char *t;
+        const char *t = NULL;
 
         assert(bus);
         assert(reply);
@@ -932,8 +932,6 @@ static int property_get_cgroup(
 
         if (u->cgroup_path)
                 t = isempty(u->cgroup_path) ? "/" : u->cgroup_path;
-        else
-                t = "";
 
         return sd_bus_message_append(reply, "s", t);
 }