LogMaterial: Error: Loading a material resource None with an invalid ShaderMap!

I have this error in the output log where it states:
LogMaterial: Error: Loading a material resource None with an invalid ShaderMap!
What is this error and how do I fix this?

@TANK123444332 Thank you for your report! We would like to look into this further, would you be able to submit a bug report using the form available here? Fortnite Creative