(FIXUP) Check for nil before injecting provider param into Types

[scotje]

cc @nkanderson

See https://forge.puppet.com/modules/enterprisemodules/ora_install/5.12.3 for an example of a module that would trigger an error before.

Error triggered was:

$ bx puppet strings generate --format json /Users/jesse/tmp/enterprisemodules-ora_install-5.12.3/ --trace
Error: undefined method `any?' for nil:NilClass
/Users/jesse/src/puppet-strings/lib/puppet-strings/yard/code_objects/type.rb:155:in `parameters'
/Users/jesse/src/puppet-strings/lib/puppet-strings/yard/code_objects/type.rb:187:in `to_hash'
/Users/jesse/src/puppet-strings/lib/puppet-strings/json.rb:16:in `map!'
/Users/jesse/src/puppet-strings/lib/puppet-strings/json.rb:16:in `render'
/Users/jesse/src/puppet-strings/lib/puppet-strings.rb:78:in `render_json'
/Users/jesse/src/puppet-strings/lib/puppet-strings.rb:59:in `generate'
...
Error: Try 'puppet help strings generate' for usage