tmpfiles: consider an argument of "-" as non-specified
diff --git a/src/tmpfiles/tmpfiles.c b/src/tmpfiles/tmpfiles.c
index b7dd37c..8cbeb67 100644
--- a/src/tmpfiles/tmpfiles.c
+++ b/src/tmpfiles/tmpfiles.c
@@ -1760,7 +1760,7 @@
                 return -EIO;
         }
 
-        if (!isempty(buffer)) {
+        if (!isempty(buffer) && !streq(buffer, "-")) {
                 i.argument = strdup(buffer);
                 if (!i.argument)
                         return log_oom();