Reading of GDML file in Geant4

Hi expert,
I was trying to read and visualise the GDML files in Geant4 (version geant4.10.05).
please find attached gdml files in this link

Here I am using the example extended/persistency/gdml/G01 example in Geant4 for this purpose.
I face following error:

Can you please suggest to resolve the issue.

Hello.

In your gdml files, you have made no material declarations for Gold. The block.gdml in the G01 example shows how to set up materials definitions. Alternatively, as gold is included in the nist database you could use the nist materials, an shown in the example file mat_nist.gdml.
For your air_gold.gdml file you would add the material tag and also change the material ref to G4_Au from Gold. Therefore the end of the file would become

  <materials>
  </materials>
  <structure>
        <volume name="air_gold">
            <materialref ref="G4_Au"/>
            <solidref ref="air_gold-SOL"/>
        </volume>
    </structure>

I hope this helps.

Thanks
Yes I realised that.
I have now added material and can read gdml files in Geant4