Analyze the provided Python script to verify the parameter mapping from a Hugging Face (HF) model to a MaxText model.

**Instructions & Rules:**
1.  **Check for Unmapped Parameters:** Identify any parameters from the HF model that are NOT mapped to a MaxText parameter by the script.
2.  **Validate Weight Tying Logic:**
    * First, determine if the model uses weight tying (the token embedding weights are the same as the `lm_head` weights).
    * **If weight tying is used,** the `lm_head.weight` parameter will likely be **absent** from the conversion script. This is correct. Verify that the script uses the **token embedding weights** for the final output layer in MaxText. The absence of a direct `lm_head.weight` mapping should **pass** validation in this case.
    * **If weight tying is NOT used,** the `lm_head.weight` parameter **must** be present in the HF list and the script **must** map it.
3.  **Provide a Clear Report:**
    * If the script is correct according to the rules above, respond with: "**Validation passed.**"
    * If there are issues, provide a bulleted list of all unmapped parameters and explain any failures in handling the weight tying logic.

**Inputs:**

* **Hugging Face Parameters:**
    `{hf_params_json}`
* **MaxText Parameters:**
    `{maxtext_params_json}`
* **Conversion Script:**
    ```python
    {code}
    ```
* **Analysis:**
{analysis}