diff --git a/inc/utils.h b/inc/utils.h
index 961936d..e2a9e87 100644
--- a/inc/utils.h
+++ b/inc/utils.h
@@ -16,6 +16,7 @@ void log_hex(rfc3161_context *ct, int priority, char *id,
 int set_params(rfc3161_context *ct, char *conf_file, char *conf_wd);
 static char *rand_string(char *str, size_t size);
 void free_uts_context(rfc3161_context *ct);
+const char *null_undef(const char * in);
 
 // some global variable to handle signals
 int g_uts_sig_up;
diff --git a/src/lib/http.c b/src/lib/http.c
index e43ea64..9565411 100644
--- a/src/lib/http.c
+++ b/src/lib/http.c
@@ -54,20 +54,20 @@ void log_request_debug(const struct mg_request_info *request_info,
     for (int i = 0; i < request_info->num_headers; i++) {
         uts_logger(context, LOG_DEBUG, "Request[%s], Header[%s]: %s",
                    request_id, request_info->http_headers[i].name,
-                   request_info->http_headers[i].value);
+                   null_undef(request_info->http_headers[i].value));
     }
     uts_logger(context, LOG_DEBUG, "Request[%s], request_method: %s",
-               request_id, request_info->request_method);
+               request_id, null_undef(request_info->request_method));
     uts_logger(context, LOG_DEBUG, "Request[%s], request_uri: %s", request_id,
-               request_info->request_uri);
+               null_undef(request_info->request_uri));
     uts_logger(context, LOG_DEBUG, "Request[%s], local_uri: %s", request_id,
-               request_info->local_uri);
+               null_undef(request_info->local_uri));
     uts_logger(context, LOG_DEBUG, "Request[%s], http_version: %s", request_id,
-               request_info->http_version);
+               null_undef(request_info->http_version));
     uts_logger(context, LOG_DEBUG, "Request[%s], query_string: %s", request_id,
-               request_info->query_string);
+               null_undef(request_info->query_string));
     uts_logger(context, LOG_DEBUG, "Request[%s], remote_addr: %s", request_id,
-               request_info->remote_addr);
+               null_undef(request_info->remote_addr));
     uts_logger(context, LOG_DEBUG, "Request[%s], is_ssl: %d", request_id,
                request_info->is_ssl);
     uts_logger(context, LOG_DEBUG, "Request[%s], content_length: %d",
@@ -97,9 +97,10 @@ void log_request(const struct mg_request_info *request_info, char *request_id,
     uts_logger(context, LOG_INFO, "Request[%s], remote_addr[%s] ssl[%d] "
                                   "uri[%s] http_resp_code[%d] duration[%d us] "
                                   "user-agent[%s] content-type[%s]",
-               request_id, request_info->remote_addr, request_info->is_ssl,
-               request_info->local_uri, response_code, timer, user_agent,
-               content_type);
+               request_id, null_undef(request_info->remote_addr),
+               request_info->is_ssl, null_undef(request_info->local_uri),
+               response_code, timer, null_undef(user_agent),
+               null_undef(content_type));
 }
 
 // This function will be called by civetweb on every new request.
diff --git a/src/lib/utils.c b/src/lib/utils.c
index 6699cb2..6bb717e 100644
--- a/src/lib/utils.c
+++ b/src/lib/utils.c
@@ -202,6 +202,12 @@ void uts_logger(rfc3161_context *ct, int priority, char *fmt, ...) {
     free(out);
 }
 
+const char *null_undef(const char * in){
+    if(in == NULL)
+        return "<undef>";
+    return in;
+}
+
 // OpenSSL file openner (use for opening the configuration file
 static BIO *bio_open_default(rfc3161_context *ct, const char *filename,
                              int format) {
@@ -281,7 +287,7 @@ int set_params(rfc3161_context *ct, char *conf_file, char *conf_wd) {
         if (value == NULL) {
             uts_logger(ct, LOG_NOTICE,
                        "configuration param['%s'] not set, using default: '%s'",
-                       name, default_value);
+                       name, null_undef(default_value));
             value = default_value;
         }
         switch (type) {
@@ -307,11 +313,11 @@ int set_params(rfc3161_context *ct, char *conf_file, char *conf_wd) {
         if (value == NULL) {
             uts_logger(ct, LOG_NOTICE,
                        "configuration param['%s'] not set, using default: '%s'",
-                       name, default_value);
+                       name, null_undef(default_value));
             value = default_value;
         }
         uts_logger(ct, LOG_DEBUG, "configuration param['%s'] = '%s'", name,
-                   value);
+                   null_undef(value));
         switch (type) {
         // if it's an http (civetweb) option, put it in the http_options buffer
         // like civetweb is expected it.