fix: fix tlsclient and tlsserver hostname cert key
diff --git a/samplecode/tls/tlsclient/enclave/src/lib.rs b/samplecode/tls/tlsclient/enclave/src/lib.rs
index 5295295..61077a0 100644
--- a/samplecode/tls/tlsclient/enclave/src/lib.rs
+++ b/samplecode/tls/tlsclient/enclave/src/lib.rs
@@ -287,7 +287,7 @@
 
 #[no_mangle]
 pub extern "C" fn tls_client_new(fd: c_int, hostname: * const c_char, cert: * const c_char) -> usize {
-    if hostname.is_null() {
+    if hostname.is_null() || cert.is_null() {
         return 0xFFFF_FFFF_FFFF_FFFF;
     }
 
diff --git a/samplecode/tls/tlsserver/enclave/src/lib.rs b/samplecode/tls/tlsserver/enclave/src/lib.rs
index 098c47d..a65b7a3 100644
--- a/samplecode/tls/tlsserver/enclave/src/lib.rs
+++ b/samplecode/tls/tlsserver/enclave/src/lib.rs
@@ -223,6 +223,10 @@
 
 #[no_mangle]
 pub extern "C" fn tls_server_new(fd: c_int, cert: * const c_char, key: * const c_char) -> usize {
+    if key.is_null() || cert.is_null() {
+        return 0xFFFF_FFFF_FFFF_FFFF;
+    }
+
     let certfile = unsafe { CStr::from_ptr(cert).to_str() };
     if certfile.is_err() {
         return 0xFFFF_FFFF_FFFF_FFFF;