Solid Filesystem basic syntax help

question about basic Filesystem usage for the Solid hex for Liquid templating. Cross-posting from Github basic Filesystem usage syntax · Issue #96 · edgurgel/solid · GitHub

what am I missing for filesystem usage in a simple Phoenix index action below?

def index(conn, _params) do
    template_path = "/lib/app_web/templates/liquid/"
    file_system = Solid.LocalFileSystem.new(template_path)
    text = Solid.LocalFileSystem.full_path(file_system, "hello")
    render(conn, text)
end

/lib/app_web/templates/liquid/_hello.liquid
hello

gives

    ** (FunctionClauseError) no function clause matching in String.match?/2
        (elixir 1.12.2) lib/string.ex:2259: String.match?(%Solid.LocalFileSystem{pattern: "_%s.liquid", root: "/lib/app_web/templates/liquid/"}, ~r/^[^.\/][a-zA-Z0-9_\/]+$/)
        (solid 0.10.0) lib/solid/file_system.ex:84: Solid.LocalFileSystem.full_path/2

no doubt missing some basic config or awareness around the correct syntax