[PATCH] perf data convert: Fix segfault when converting to json on arm64

[Ilkka Koskinen <ilkka@os.amperecomputing.com>]

Arm64 doesn't have Model in /proc/cpuinfo and, thus, cpu_desc doesn't get
assigned.

Running
	$ perf data convert --to-json perf.data.json

ends up calling output_json_string() with NULL pointer, which causes a
segmentation fault.

Signed-off-by: Ilkka Koskinen <ilkka@os.amperecomputing.com>
---
 tools/perf/util/data-convert-json.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tools/perf/util/data-convert-json.c b/tools/perf/util/data-convert-json.c
index 5bb3c2ba95ca..5d6de1cef546 100644
--- a/tools/perf/util/data-convert-json.c
+++ b/tools/perf/util/data-convert-json.c
@@ -97,6 +97,11 @@ static void output_json_format(FILE *out, bool comma, int depth, const char *for
 static void output_json_key_string(FILE *out, bool comma, int depth,
 		const char *key, const char *value)
 {
+	if (!value) {
+		pr_info("No value set for key %s\n", key);
+		return;
+	}
+
 	output_json_delimiters(out, comma, depth);
 	output_json_string(out, key);
 	fputs(": ", out);
-- 
2.43.0