[TextmeshPro] NullReferenceException error is thrown on changing Vertex color property in TextMeshPro preset asset.

NullReferenceException error is thrown on changing Vertex color property in TextMeshPro preset asset after deleting TextMeshPro text from the Hierarchy.

Steps to repro:
1. Create a new project.
2. GameObject > 3D Object > Text - TextMeshPro > Import TMP Essentials And Import TMP Examples & Extras.
3. Create Preset of TextMeshPro-Text.
4. Delete TextMeshPro-Text object from the Hierarchy.
5. Change Vertex Color property in the preset asset.

Actual Result:
NullReferenceException error is thrown in the console.

Expected Result:
No error in the console.

Reproducible with Unity Version:
2020.1.0a15, 2019.3.0f1.

Reproducible with Package Version: 2.0.1, 2.0.0, 1.4.1, 1.4.0.

Working Fine with Package version: 1.2.1

Environment:
Windows 10 & Mac 10.14.

Stack trace:
NullReferenceException: Object reference not set to an instance of an object
TMPro.TextMeshPro.UpdateMaterial () (at library/packagecache/com.unity.textmeshpro@2.0.1/scripts/runtime/textmeshpro.cs:269)
TMPro.TextMeshPro.SetMaterialDirty () (at library/packagecache/com.unity.textmeshpro@2.0.1/scripts/runtime/textmeshpro.cs:206)
TMPro.TextMeshPro.SetAllDirty () (at library/packagecache/com.unity.textmeshpro@2.0.1/scripts/runtime/textmeshpro.cs:220)
TMPro.TMP_Text.set_havePropertiesChanged (System.Boolean value) (at library/packagecache/com.unity.textmeshpro@2.0.1/scripts/runtime/tmp_text.cs:1034)
TMPro.EditorUtilities.TMP_BaseEditorPanel.OnInspectorGUI () (at library/packagecache/com.unity.textmeshpro@2.0.1/scripts/editor/tmp_baseeditorpanel.cs:267)
UnityEditor.Presets.PresetEditor.DrawInternalInspector () (at <3b74787e58694cdda2c241162159b3b7>:0)
UnityEditor.Presets.PresetEditor.DrawPresetData () (at <3b74787e58694cdda2c241162159b3b7>:0)
UnityEditor.Presets.PresetEditor.OnInspectorGUI () (at <3b74787e58694cdda2c241162159b3b7>:0)
UnityEditor.UIElements.InspectorElement+<>c__DisplayClass55_0.<CreateIMGUIInspectorFromEditor>b__0 () (at <3b74787e58694cdda2c241162159b3b7>:0)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)