How to use go.set() to set a vertex attribute of type Mat3?

I am trying to pass a Texture Transform 2D to my vertex shader. I set the Vertex Attribute in the material, have it declared and used in the shader. But when I try to set it using go.set("#model", "transform2d", vmath.matrix4()) I get the error:

ERROR:SCRIPT: main/script.script:2: the property 'transform2d' of '#model' must be a boolean

In the Material Manual, last paragraph of the section “Setting custom vertex attribute data” my understanding is that I should be using a vmath.matrix4(). The example given is actually very close to what I am trying to do but it doesn’t show the lua code for how to set the attribute.

Here is a reproduction of the problem

set_texture_transform_test.zip (32.6 KB)