(C#) Problem with SerializedProperty. FindPropertyRelative returning null in Unity

I am struggling to create a custom editor in Unity.
However, I am currently experiencing a problem that I cannot access other member variables inside the TalkerCharacter type variable found through the FindPropertyRelative function.
Below is some of the code I wrote.
In the Debug.Log part, "NullReferenceException: Object reference not set to an instance of an object" error occurs.
I apologize for my weak English skills. Any help would be appreciated.

[System.Serializable]
public class TalkerMessage : ScriptableObject
{
    public TalkerScript[] scripts;
}

[System.Serializable]
public class TalkerScript
{
    public string text = "123";
    [Space(30)]
    public TalkerCharacter character = new TalkerCharacter();
    public string face = "";

    public TalkerScript(TalkerCharacter chr, string txt)
    {
        this.character = chr;
        this.text = txt;
    }
}

[Serializable]
public class TalkerCharacter : ScriptableObject
{
    public new string name = "";
    public TalkerFace[] faces = new TalkerFace[10];
    //public enum FACE { Normal, Smile, Etc1, Etc2, Etc3, Etc4, Etc5 , Etc6 , Etc7 , Etc8 , Etc9, Etc10 }
    //public Tuple<string, Sprite>[] faces = new Tuple<string, Sprite>[20];
    //public Sprite[] illust = new Sprite[System.Enum.GetNames(typeof(FACE)).Length];
    //public string dict = "";
    public TalkerCharacter()
    {
        name = "";
        faces = new TalkerFace[10];
    }
}

[CustomEditor(typeof(TalkerMessage))]
[System.Serializable]
public class TalkerMessageEditor : Editor 
{
    private Vector2 scrollPos = Vector2.zero;
    [SerializeField]
    private TalkerCharacter character;
    TalkerMessage other;
    SerializedProperty m_script;
    private ReorderableList scriptList;
    
    void OnEnable()
    {
        other = target as TalkerMessage;
        m_script = serializedObject.FindProperty("scripts");
        scriptList = new ReorderableList(serializedObject, m_script, true, true, true, true);

        scriptList.elementHeight = 60 + EditorGUIUtility.singleLineHeight;
        scriptList.drawElementCallback = (Rect rect, int index, bool isActive, bool isFocused) =>
        {
            SerializedProperty element = scriptList.serializedProperty.GetArrayElementAtIndex(index);
            if (element != null)
            {
                rect.y += 2;
                SerializedProperty prop = element.FindPropertyRelative("character");
                Debug.Log(prop.FindPropertyRelative("name").ToString());
                EditorGUI.PropertyField(new Rect(rect.x, rect.y + EditorGUIUtility.singleLineHeight, 60, 60), element.FindPropertyRelative("face"), GUIContent.none);
                EditorGUI.TextArea(new Rect(rect.x + 60, rect.y + EditorGUIUtility.singleLineHeight, EditorGUIUtility.currentViewWidth - 260, 60), "12321");
            }
        };
    }
}

In this code, the serialized version of the character variable found with FindPropertyRelative shows up as non-null when printed to Debug.Log, but when I try to use FindPropertyRelative once more with this variable to access any other variable within it, an error occurs.

Your further nested elements of TalkerCharacter are all ScriptableObject assets and not normal serialized classes such as the TalkerScript.

=> For those the prop actually only contains an objectReferenceValue.

In order to dive deeper into that one you need to create a temporary SerailizedObject of it again like e.g.

SerializedProperty element = scriptList.serializedProperty.GetArrayElementAtIndex(index);

rect.y += 2;
var prop = element.FindPropertyRelative("character");
if(prop.objectReferenceValue)
{
    var so = new SerializedObject(prop.objectReferenceValue);   
    Debug.Log(so.FindProperty("name").stringValue);
    EditorGUI.PropertyField(new Rect(rect.x, rect.y + EditorGUIUtility.singleLineHeight, 60, 60), element.FindPropertyRelative("face"), GUIContent.none);
    EditorGUI.TextArea(new Rect(rect.x + 60, rect.y + EditorGUIUtility.singleLineHeight, EditorGUIUtility.currentViewWidth - 260, 60), "12321");
}

In general I would avoid to hide/shadow the built-in UnityEngine.Object.name property. Rather use a different field name like characterName or don't use a custom field at all but simply stick to the built-in one. It equals at the same time the actual asset name so actually it is quite handy to just stick to that and name your characters directly already on the ScriptableObject name itself.