Can't pass undef as a param value

[jmoldow]

When testing a definition or parametrized class, it isn't possible to use let(:params) to set one of the values to Puppet's undef value.

One might try doing something like let(:params) { { :foo => nil } }, but this doesn't work. When constructing the declaration, the value is inspected to a string, which in this case is 'nil'. The resource declaration that is constructed is class { 'test': foo => nil }, which is not valid Puppet and caused an error to be raised.

Doing something like let(:params) { { :foo => :undef } } is similarly invalid. And doing something like let(:params) { { :foo => 'undef' } } leads to the resource declaration class { 'test': foo => "undef" }, which is valid but doesn't actually use the special undef value.

When nil is used as a param value, it should not be inspected, but should instead lead to the string 'undef' being used in the generated resource declaration.

Another solution, proposed at the end of [1], would be to define a special Undef class whose inspect method returns the unquoted string 'undef'. Then let(:params) { { :foo => Undef.new } } leads to the desired resource declaration class { 'test': foo => undef }.

I believe the first solution is better and more developer friendly, because it uses the Ruby native nil value and doesn't introduce any extra types that developers need to know about. And after all, Puppet undef is nearly equivalent to Ruby nil, so it makes sense to do this translation.

[1] https://groups.google.com/forum/#!topic/puppet-users/6nL2eROH8is