Fixing nits

Signed-off-by: Vladimir Suvorov <suvorovv@google.com>

Author: mydatascience

src/MaxText/examples/rl_llama3_demo.ipynb

@@ -117,7 +117,10 @@
     "if not MODEL_CHECKPOINT_PATH:\n",
     "    raise RuntimeError(\"MODEL_CHECKPOINT_PATH is not set\")\n",
     "    \n",
-    "OUTPUT_DIRECTORY = \"/tmp/gpo_output\"  # Update this!\n",
+    "OUTPUT_DIRECTORY = \"\"  # Update this!\n",
+    "if not OUTPUT_DIRECTORY:\n",
+    "    raise RuntimeError(\"OUTPUT_DIRECTORY is not set\")\n",
+    "    \n",
     "os.environ[\"HF_TOKEN\"] = HF_TOKEN\n",
     "\n",
     "if HF_TOKEN:\n",