safeDump crashes with obscure "unknown reason" if JSON contains undefined

[pelotom]

For example:

yaml.safeDump({ foo: undefined })

throws

(unknown reason)

      at writeNode (node_modules/js-yaml/lib/js-yaml/dumper.js:731:13)
      at writeBlockMapping (node_modules/js-yaml/lib/js-yaml/dumper.js:610:10)
      at writeNode (node_modules/js-yaml/lib/js-yaml/dumper.js:703:9)
      at dump (node_modules/js-yaml/lib/js-yaml/dumper.js:792:7)
      at Object.safeDump (node_modules/js-yaml/lib/js-yaml/dumper.js:798:10)
      ...

It's not clear what should happen, but any of these seem like better alternatives:

• Treat the key as absent if undefined is found as a value in an object
• Treat it the same as null
• Make the error message more descriptive: "Encountered undefined value in JSON" or somesuch

[puzrin]

undefined is not valid value for JSON & YAML. You passed JS object, not JSON.

But i agree, dumper could be more nice.

@dervus ?

[MunifTanjim]

JSON.stringify removes the key-pair with undefined value.

yaml.safeDump should do the same.

[rlidwka]

Fixed in 56d5616 (currently in dev branch).

Now undefined follows roughly the same black magic as in JSON:

• replaced with null in collections (errors out if null isn't in the schema)
• removed from mappings entirely if either key or value is undefined

If user defines custom schema for undefined, it serializes as before.