send-email: don't call methods on undefined values

diff --git a/trace.c b/trace.c
index 5ec0e3bd16b5cfc59254c6e10d4555ef3029aa36..3d744d1d4d93e7d4770ce858a7d5aee1c955a82b 100644 (file)
--- a/trace.c
+++ b/trace.c
@@ -75,6 +75,7 @@ static void trace_vprintf(const char *key, const char *fmt, va_list ap)
        strbuf_release(&buf);
 }
 
+__attribute__((format (printf, 2, 3)))
 static void trace_printf_key(const char *key, const char *fmt, ...)
 {
        va_list ap;