Reproduction steps:
1. Open the attached “TextGlyph.zip” project
2. Select the “Text (TMP)” GameObject in the “Canvas” in the Hierarchy
3. Expand “Extra Settings” in the TMP Component in the Inspector
4. Double-click on the attached Sprite Asset
5. Expand the “Sprite Character Table” in the Inspector
6. Click on any of the Sprites
7. Click “Edit Glyph”

Expected result: Glyph editing panel appears and no errors are thrown
Actual result: “NullReferenceException” errors are thrown and the Inspector freezes

Reproducible with: 2023.2.0a14, 2023.2.11f1, 2023.3.0b8
Not reproducible with: 2021.3.35f1, 2022.3.20f1, 2023.2.0a13

Reproducible on: Windows 10 (User reported), Windows 11
Not reproducible on: no other environment tested

Notes:
- Make sure to import TMP Essentials
- When the Inspector freezes after “Edit Glyph” is clicked, clicking on any other GameObject unfreezes the Inspector
- Longer error text: “NullReferenceException: Object reference not set to an instance of an object
TMPro.EditorUtilities.TMP_SpriteCharacterPropertyDrawer.OnGUI (UnityEngine.Rect position, UnityEditor.SerializedProperty property, UnityEngine.GUIContent label) (at ./Library/PackageCache/com.unity.ugui/Editor/TMP/PropertyDrawers/TMP_SpriteCharacterPropertyDrawer.cs:132)”