Fix NULL argument handling in mbedtls_xxx_free() functions

Signed-off-by: Troy-Butler <squintik@outlook.com>
diff --git a/library/ssl_ticket.c b/library/ssl_ticket.c
index 6a31b0b..bfb656c 100644
--- a/library/ssl_ticket.c
+++ b/library/ssl_ticket.c
@@ -534,6 +534,10 @@
  */
 void mbedtls_ssl_ticket_free(mbedtls_ssl_ticket_context *ctx)
 {
+    if (ctx == NULL) {
+        return;
+    }
+
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
     psa_destroy_key(ctx->keys[0].key);
     psa_destroy_key(ctx->keys[1].key);