fix: handle null or undefined content when parsing markdown in bot messages

index.html

@@ -384,7 +384,7 @@
             contentDiv.className = 'message-content';
             
             if (role === 'bot') {
-                contentDiv.innerHTML = marked.parse(content);
+                contentDiv.innerHTML = marked.parse(content || "");
             } else {
                 contentDiv.textContent = content;
             }
@@ -438,7 +438,7 @@
                             typingIndicator.style.display = 'none';
                         }
                         fullResponse = event.data[0];
-                        botContentDiv.innerHTML = marked.parse(fullResponse);
+                        botContentDiv.innerHTML = marked.parse(fullResponse || "");
                         scrollToBottom();
                     }
                     if (event.type === "status") {