Error with call to IsSet

[Icifra]

When using one of the themes and extended Hugo on the command line, I get the following error:

Tell me, please, what is it and how does it affect the assembly of the site?

[jmooring]

site configuration

[params.a]
x = 1

template

{{ site.Params.a | printf "%T" }} --> maps.Params
{{ isset site.Params.a "x" }} --> true

{{ site.Params.b | printf "%T" }} --> <nil>
{{ isset site.Params.b "x" }} --> false (emits warning: calling IsSet with unsupported type "invalid" (<nil>) will always return false)

The right way to handle this:

{{ if site.Params.b }}
  ...
{{ end }}

Please raise an issue with the theme author.