If you have a texture attached to a node in a shader graph, setting the texture to 'None' will not update the preview in the node.

Repro:
1. Create a new unity project.
2. Install Shader Graph package through package manager. (Window -> Package Manager)
3. Create a new shader graph. (i.e. Assets -> Create -> Shader -> Unlit Graph)
4. Open the shader graph.
5. Create a Sample Texture 2D in the shader graph window. (Right Click -> Create Node, search for 'Sample Texture 2D')
6. Set the Texture on this node to any texture.
7. Set the Texture to 'None'.

Expected Outcome: The texture preview is updated.
Actual Outcome: The previously set texture remains visible in the preview. GIF attached to case.

Package found version 6.9.1, can reproduce in 7.0.1, 7.1.1
Not reproducible in package version 5.2.3