diff --git a/src/ngx_http_ssl_ja4_module.h b/src/ngx_http_ssl_ja4_module.h
index 12f2c16..51ce2fc 100644
--- a/src/ngx_http_ssl_ja4_module.h
+++ b/src/ngx_http_ssl_ja4_module.h
@@ -354,10 +354,19 @@ ngx_ssl_ja4_detail_print(ngx_pool_t *pool, ngx_ssl_ja4_t *ja4)
     }
 
     /* ALPN Values */
-    ngx_log_debug1(NGX_LOG_DEBUG_EVENT,
-                   pool->log, 0, "ssl_ja4: ALPN Value: %s\n",
-                   ja4->alpn_first_value);
-}
+    // handle if null
+    if (ja4->alpn_first_value == NULL)
+    {
+        ngx_log_debug1(NGX_LOG_DEBUG_EVENT,
+                       pool->log, 0, "ssl_ja4: ALPN Value: NULL\n");
+    }
+    else
+    {
+        ngx_log_debug1(NGX_LOG_DEBUG_EVENT,
+                       pool->log, 0, "ssl_ja4: ALPN Value: %s\n",
+                       ja4->alpn_first_value);
+    }
+    
 #endif
 
 // FUNCTION PROTOTYPES