MissingReferenceException is thrown in the console and Material is deleted on changing several options from "Overflow" property dropdown under "Text Mesh Pro UGUI (Script)" component

Steps to repro:
1. Create a new project
2. Window > TextMeshPro > Import TMP Essential Resources
3. Hierarchy > Create > UI > TextMeshPro - Text
4. Click on "TextMeshPro Text" object in Hierarchy
5. Add text in "Text Field" under "Text Mesh Pro UGUI (Script)" component such that text exceeds bounds.
6. Change several options from "Overflow" property dropdown from "Text Mesh Pro UGUI (Script)" component

Actual Result:
MissingReferenceException has thrown while selecting options from Overflow dropdown

Expected Result:
Options under Overflow dropdown can be selected without any errors in the console

Reproducible on:
2019.2.0a3, 2019.1.0b1, 2018.3.0f2, 2018.2.0f2, 2018.1.0f2, 2018.1.0b5

Package versions:
1.3.0, 1.2.0, 1.1.0, 0.1.2

Note:
1. TextMeshPro package introduced in 2018.1.0b5
2. Refer attached video

Environment:
Windows & Mac

Stack Trace:
MissingReferenceException: The object of type 'Material' has been destroyed but you are still trying to access it.
Your script should either check if it is null or you should not destroy the object.
TMPro.TextMeshProUGUI.GenerateTextMesh () (at Library/PackageCache/com.unity.textmeshpro@1.3.0/Scripts/Runtime/TMPro_UGUI_Private.cs:2080)
TMPro.TextMeshProUGUI.GenerateTextMesh () (at Library/PackageCache/com.unity.textmeshpro@1.3.0/Scripts/Runtime/TMPro_UGUI_Private.cs:2691)
TMPro.TextMeshProUGUI.OnPreRenderCanvas () (at Library/PackageCache/com.unity.textmeshpro@1.3.0/Scripts/Runtime/TMPro_UGUI_Private.cs:1642)
TMPro.TextMeshProUGUI.Rebuild (UnityEngine.UI.CanvasUpdate update) (at Library/PackageCache/com.unity.textmeshpro@1.3.0/Scripts/Runtime/TextMeshProUGUI.cs:209)
UnityEngine.UI.CanvasUpdateRegistry.PerformUpdate () (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/UI/Core/CanvasUpdateRegistry.cs:198)
UnityEngine.Canvas:SendWillRenderCanvases()