#6 nil emited as an empty string

[Anonymous]

nil is emited as an empty string. This produces
incorrect YAML output.

So YAML::load({nil=>nil}.to_yaml) fails.

Proposed change in yaml/rubytypes.rb:

class NilClass
def is_complex_yaml?
false
end
def to_yaml( opts = {} )
opts[:KeepValue] = true
"~".to_yaml( opts ) # "~" instead of ""
end
end