fileio: automatically add NULL sentinel to parse_env_file()

Let's modernize things a bit.

src/basic/fileio.c

@@ -710,7 +710,7 @@ int parse_env_filev(
         return n_pushed;
 }
 
-int parse_env_file(
+int parse_env_file_sentinel(
                 FILE *f,
                 const char *fname,
                 ...) {

src/basic/fileio.h

@@ -43,7 +43,8 @@ int read_full_stream(FILE *f, char **contents, size_t *size);
 int verify_file(const char *fn, const char *blob, bool accept_extra_nl);
 
 int parse_env_filev(FILE *f, const char *fname, va_list ap);
-int parse_env_file(FILE *f, const char *fname, ...) _sentinel_;
+int parse_env_file_sentinel(FILE *f, const char *fname, ...) _sentinel_;
+#define parse_env_file(f, fname, ...) parse_env_file_sentinel(f, fname, __VA_ARGS__, NULL)
 int load_env_file(FILE *f, const char *fname, char ***l);
 int load_env_file_pairs(FILE *f, const char *fname, char ***l);
 

src/basic/util.c

@@ -248,7 +248,9 @@ int container_get_leader(const char *machine, pid_t *pid) {
                 return -EINVAL;
 
         p = strjoina("/run/systemd/machines/", machine);
-        r = parse_env_file(NULL, p, "LEADER", &s, "CLASS", &class, NULL);
+        r = parse_env_file(NULL, p,
+                           "LEADER", &s,
+                           "CLASS", &class);
         if (r == -ENOENT)
                 return -EHOSTDOWN;
         if (r < 0)