Merge branch 'di/fast-import-empty-tag-note-fix'

* di/fast-import-empty-tag-note-fix:
  fast-import: don't allow to note on empty branch
  fast-import: don't allow to tag empty branch

fast-import.c

@@ -2411,6 +2411,8 @@ static void note_change_n(struct branch *b, unsigned char old_fanout)
 	/* <committish> */
 	s = lookup_branch(p);
 	if (s) {
+		if (is_null_sha1(s->sha1))
+			die("Can't add a note on empty branch.");
 		hashcpy(commit_sha1, s->sha1);
 	} else if (*p == ':') {
 		uintmax_t commit_mark = strtoumax(p + 1, NULL, 10);
@@ -2712,6 +2714,8 @@ static void parse_new_tag(void)
 	from = strchr(command_buf.buf, ' ') + 1;
 	s = lookup_branch(from);
 	if (s) {
+		if (is_null_sha1(s->sha1))
+			die("Can't tag an empty branch.");
 		hashcpy(sha1, s->sha1);
 		type = OBJ_COMMIT;
 	} else if (*from == ':') {

t/t9300-fast-import.sh

@@ -820,6 +820,18 @@ test_expect_success \
 	'test 1 = `git rev-list J | wc -l` &&
 	 test 0 = `git ls-tree J | wc -l`'
 
+cat >input <<INPUT_END
+reset refs/heads/J2
+
+tag wrong_tag
+from refs/heads/J2
+data <<EOF
+Tag branch that was reset.
+EOF
+INPUT_END
+test_expect_success \
+	'J: tag must fail on empty branch' \
+	'test_must_fail git fast-import <input'
 ###
 ### series K
 ###
@@ -1975,6 +1987,23 @@ test_expect_success \
 	'Q: verify second note for second commit' \
 	'git cat-file blob refs/notes/foobar:$commit2 >actual && test_cmp expect actual'
 
+cat >input <<EOF
+reset refs/heads/Q0
+
+commit refs/heads/note-Q0
+committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+data <<COMMIT
+Note for an empty branch.
+COMMIT
+
+N inline refs/heads/Q0
+data <<NOTE
+some note
+NOTE
+EOF
+test_expect_success \
+	'Q: deny note on empty branch' \
+	'test_must_fail git fast-import <input'
 ###
 ### series R (feature and option)
 ###