On exporting Custom Render Texture from its preset then it causes the editor to throw ArgumentException, Refer attached video.

Steps to repro:
1. Create a new project.
2. Project > Create > Custom Render Texture
3. Create Preset of Custom Render Texture
4. CustomRenderTexture preset > Inspector > Burger Button > Export

Actual Result:
ArgumentException is thrown on exporting Custom Render Texture from its preset

Expected Result:
Custom Render Texture is export gracefully

Reproducible in:
2021.1.0a1, 2020.2.0b7, 2020.1.7f1, 2019.4.10f1, 2018.4.27f1

Environment:
Windows10 and macOS 10.15

Stack trace:
ArgumentException: Invalid path
System.IO.Path.GetDirectoryName (System.String path) (at <9577ac7a62ef43179789031239ba8798>:0)
UnityEditor.CustomRenderTextureEditor.SaveToDisk (UnityEditor.MenuCommand command) (at <859685c8158c480a8d135de9619162c9>:0)