USD Import - Import unbound materials and shaders

[mPoittevinAtSP]

Hello all,

My team and I are currently working on building a Material Bank based on the USD file format, and as Maya is one of the main DCCs we are using in our pipeline, we want to be able to import the generic materials from our Material Bank (described using USD files) inside Maya.
In order to remain as generic as possible, the USD files describing the materials are very basic, and do not contain any geometry data, nor binding data. The idea is to describe solely materials inside each USD file composing the Material Bank.

The problem we have is, when importing these USD files inside Maya 2022, using the cmds.file(type='USD Import') python command, no node is generated. The materials aren't imported in the Maya scene, nor the shader nodes or textures.

However, as soon as a single geometry is described in the USD file, and the materials bound to it, then the problem described above disappears, and nodes are correctly generated in the scene, as expected (materials, shaders and textures are correctly imported from the USD file).

My question is : is this an expected behaviour than not to import USD materials which are not bound to any geometry ?
And if not, which would be the recommended go-to process to import USD files describing only materials (with absolutely no geometry info, nor binding info) inside a Maya scene, and having the nodes correctly generated ?

More details on the import process we are currently using :

• Our USD files were generated from Solaris.
• These files contain both USD Preview Surface Shaders and Arnold Standard Surface Shaders.
• These files contain both USD Uv Textures and Arnold images nodes.
• The USD import command used is the following :

cmds.file(
       pathToUSDFile,
        i=True,
        type="USD Import",
        returnNewNodes=True,
        defaultNamespace=True,
    )

Thanks a lot in advance for your feedback, and your time.