tree-wide: introduce mfree()

Pretty trivial helper which wraps free() but returns NULL, so we can
simplify this:
        free(foobar);
        foobar = NULL;
to this:
        foobar = mfree(foobar);

1 files changed, 2 insertions, 4 deletions

diff --git a/src/core/main.c b/src/core/main.c
index 6ae8b51544..a66fb18418 100644
--- a/src/core/main.c
+++ b/src/core/main.c
@@ -1844,13 +1844,11 @@ finish:
                 arg_default_rlimit[j] = NULL;
         }
 
-        free(arg_default_unit);
-        arg_default_unit = NULL;
+        arg_default_unit = mfree(arg_default_unit);
 
         free_join_controllers();
 
-        strv_free(arg_default_environment);
-        arg_default_environment = NULL;
+        arg_default_environment = strv_free(arg_default_environment);
 
         set_free(arg_syscall_archs);
         arg_syscall_archs = NULL;