How to use GetMaterials function with skinned mesh renderer

I’m trying to get the materials from the skinned mesh renderer using the ‘GetMaterials’ function but it wants a parameter ‘m’ that corresponds to a list. Here is the error:
There is no argument given that corresponds to the required formal parameter ‘m’ of ‘Renderer.GetMaterials(List).’
I am trying to get the materials to reassign them at runtime. I’m trying to avoid just calling the materials function because I recognize that GetMaterials is better for performance. What parameter should be used for this function? 'preciate it.

Just came across this 11 years later but for anyone who is still having this issue it works like this

MeshRenderer meshRenderer = GetComponent<MeshRenderer>();
List<Material> materials = new List<Material>();
meshRenderer.GetMaterials(materials);