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Maniphest T95280

Applying Geometry Nodes modifier creates a new empty material slot on the resulting mesh
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Description

System Information
Operating system: Windows-10-10.0.19044-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 2080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 496.76

Blender Version
Broken: version: 3.1.0 Alpha, branch: master, commit date: 2022-01-23 19:27, hash: rBabf30007abda
Worked: (newest version of Blender that worked as expected)

Short description of error
In some circumstances, when applying GN modifier or converting GN object to mesh, this operation will add a new, empty material slot on the top of the material slot stack. This creates significant issues when exporting GN-generated object to external game engines, where proper material assignment relies on consistent material slot order.
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Exact steps for others to reproduce the error

  1. Open the attached .blend file:
    MatSlotBug.zip98 KBDownload
  2. Observe there is only one material slot on the object and it contains the same material which is assigned through GN.
  3. Apply the GN modifier on the object

Result: Applying the GN modifier adds a new, empty material slot on top of the material slot list
Expected: Applying the GN modifier does not cause creation of new, empty material slots.

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