Gazebo not converting base_link <gazebo ref> data

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Hi,

I'm testing some gazebo physics and I needed to change the friction of simple shapes.

I started applying friction to a caster wheel, for example, by using the tag <gazebo> and it works as expected.

Although, if I try to set the same <mu1> or <mu2> to a base link (the first link of my model), it does not work.

I'm using gazebo 11.5.1 and executing the command

gz sdf -p test.urdf > test.sdf

The input: https://gist.github.com/marcoarruda/0...

The output: https://gist.github.com/marcoarruda/9...