v2log: Handle new repository case.

diff --git a/builtin/log.c b/builtin/log.c
index 4f1b42a..1685946 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -355,6 +355,15 @@ static int git_log_config(const char *var, const char *value, void *cb)
 	return git_diff_ui_config(var, value, cb);
 }
 
+static const char *default_to_head_if_exists(void)
+{
+	unsigned char sha1[20];
+	if (resolve_ref_unsafe("HEAD", sha1, 1, NULL))
+		return "HEAD";
+	else
+		return NULL;
+}
+
 int cmd_whatchanged(int argc, const char **argv, const char *prefix)
 {
 	struct rev_info rev;
@@ -366,7 +375,7 @@ int cmd_whatchanged(int argc, const char **argv, const char *prefix)
 	rev.diff = 1;
 	rev.simplify_history = 0;
 	memset(&opt, 0, sizeof(opt));
-	opt.def = "HEAD";
+	opt.def = default_to_head_if_exists();
 	cmd_log_init(argc, argv, prefix, &rev, &opt);
 	if (!rev.diffopt.output_format)
 		rev.diffopt.output_format = DIFF_FORMAT_RAW;
@@ -459,7 +468,7 @@ int cmd_show(int argc, const char **argv, const char *prefix)
 	rev.diffopt.stat_width = -1; 	/* Scale to real terminal size */
 
 	memset(&opt, 0, sizeof(opt));
-	opt.def = "HEAD";
+	opt.def = default_to_head_if_exists();
 	opt.tweak = show_rev_tweak_rev;
 	cmd_log_init(argc, argv, prefix, &rev, &opt);
 
@@ -532,7 +541,7 @@ int cmd_log_reflog(int argc, const char **argv, const char *prefix)
 	init_reflog_walk(&rev.reflog_info);
 	rev.verbose_header = 1;
 	memset(&opt, 0, sizeof(opt));
-	opt.def = "HEAD";
+	opt.def = default_to_head_if_exists();
 	cmd_log_init_defaults(&rev);
 	rev.abbrev_commit = 1;
 	rev.commit_format = CMIT_FMT_ONELINE;
@@ -553,8 +562,13 @@ int cmd_log(int argc, const char **argv, const char *prefix)
 	init_revisions(&rev, prefix);
 	rev.always_show_header = 1;
 	memset(&opt, 0, sizeof(opt));
-	opt.def = "HEAD";
+	opt.def = default_to_head_if_exists();
+
 	cmd_log_init(argc, argv, prefix, &rev, &opt);
+
+	if (!opt.def && !rev.cmdline.nr)
+		return 0;
+
 	return cmd_log_walk(&rev);
 }
 
@@ -1128,7 +1142,7 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 	DIFF_OPT_SET(&rev.diffopt, RECURSIVE);
 	rev.subject_prefix = fmt_patch_subject_prefix;
 	memset(&s_r_opt, 0, sizeof(s_r_opt));
-	s_r_opt.def = "HEAD";
+	s_r_opt.def = default_to_head_if_exists();
 
 	if (default_attach) {
 		rev.mime_boundary = default_attach;