json: Avoid calling strlen(NULL)

MIME parts may have no filename, which previously resulted in calling
strlen(NULL).

1 files changed, 3 insertions, 0 deletions

diff --git a/json.c b/json.c
index 1d0c1694..3fd923ca 100644
--- a/json.c
+++ b/json.c
@@ -105,5 +105,8 @@ json_quote_chararray(const void *ctx, const char *str, const size_t len)
 char *
 json_quote_str(const void *ctx, const char *str)
 {
+    if (str == NULL)
+	str = "";
+
     return (json_quote_chararray (ctx, str, strlen (str)));
 }