node_params key => :undef not passed properly to puppet

[MorningLightMountain713]

I have the following excerpt from a spec:

context "with no default algorithm set" do
  let(:node_params) do
    super().merge(
      'foo::default_algorithm' => :undef,
    )
  end
  it { is_expected.to 
    compile.and_raise_error(%r{.*default algorithm must be set.*}) }
end

and the following in a puppet class:

class foo::bar {
  $default_algorithm = $foo::default_algorithm
  if (!$default_algorithm) {
    fail("default algorithm must be set")
  }
}

I would expect that the test should pass however the catalogue compiles instead of raising an error as the :undef symbol is seen as the string 'undef' so the if statement evaluates to true.

The way around this is to change my puppet code to be:

if ($default_algorithm == undef or $default_algorithm == 'undef') {