refs: handle zero oid for pseudorefs

diff --git a/refs.c b/refs.c
index 7820a52c4f4362829a95f73e5899451c486b2c35..26af07fc51791e511200c5011e8655822be18337 100644 (file)
--- a/refs.c
+++ b/refs.c
@@ -681,9 +681,19 @@ static int write_pseudoref(const char *pseudoref, const struct object_id *oid,
        if (old_oid) {
                struct object_id actual_old_oid;
 
-               if (read_ref(pseudoref, &actual_old_oid))
-                       die("could not read ref '%s'", pseudoref);
-               if (oidcmp(&actual_old_oid, old_oid)) {
+               if (read_ref(pseudoref, &actual_old_oid)) {
+                       if (!is_null_oid(old_oid)) {
+                               strbuf_addf(err, "could not read ref '%s'",
+                                           pseudoref);
+                               rollback_lock_file(&lock);
+                               goto done;
+                       }
+               } else if (is_null_oid(old_oid)) {
+                       strbuf_addf(err, "ref '%s' already exists",
+                                   pseudoref);
+                       rollback_lock_file(&lock);
+                       goto done;
+               } else if (oidcmp(&actual_old_oid, old_oid)) {
                        strbuf_addf(err, "unexpected object ID when writing '%s'",
                                    pseudoref);
                        rollback_lock_file(&lock);