"Cannot set property 'x-alternatives' of undefined" for .when without a then: clause

Context

• Hapi-swagger version: 7.2.0
• Joi version: 9.0.4

What are you trying to achieve or the steps to reproduce ?

I have the following validation with Joi 9.0.4. Joi allows when clauses with either ‘then’ or ‘otherwise’ but it seems to raise errors in the latest version of hapi-swagger

tagName: joi.string().when('parentType', {
            is: 'tag',
            otherwise: joi.allow(null)
        }).required().description('Name of the tag where the document was found.  Only applicable if parentType == tag'),

What result did you get?

I get the following error when I try to load the swagger JSON

TypeError: Uncaught error: Cannot set property 'x-alternatives' of undefined
    at internals.properties.parseProperty.internals.properties.parseString.internals.properties.parseObject.internals.properties.parseAlternatives.joiObj._inner.matches.reduce [as parseAlternatives] (/Users/timjones/gyda/haakon-env/repos/node-tracking/node_modules/hapi-swagger/lib/properties.js:496:40)
    at internals.properties.parseProperty.isAlt [as parseProperty] (/Users/timjones/gyda/haakon-env/repos/node-tracking/node_modules/hapi-swagger/lib/properties.js:180:25)
    at /Users/timjones/gyda/haakon-env/repos/node-tracking/node_modules/hapi-swagger/lib/properties.js:361:45
    at Array.forEach (native)
    at internals.properties.parseProperty.internals.properties.parseString.internals.properties.parseObject.isAlt [as parseObject] (/Users/timjones/gyda/haakon-env/repos/node-tracking/node_modules/hapi-swagger/lib/properties.js:351:12)
    at internals.properties.parseProperty.isAlt [as parseProperty] (/Users/timjones/gyda/haakon-env/repos/node-tracking/node_modules/hapi-swagger/lib/properties.js:139:29)
    at internals.paths.build.internals.paths.buildRoutes.internals.paths.getSwaggerStructures (/Users/timjones/gyda/haakon-env/repos/node-tracking/node_modules/hapi-swagger/lib/paths.js:451:41)
    at /Users/timjones/gyda/haakon-env/repos/node-tracking/node_modules/hapi-swagger/lib/paths.js:209:38
    at Array.forEach (native)
    at internals.paths.build.internals.paths.buildRoutes.routes [as buildRoutes] (/Users/timjones/gyda/haakon-env/repos/node-tracking/node_modules/hapi-swagger/lib/paths.js:179:12)
    at internals.paths.build.routes.forEach [as build] (/Users/timjones/gyda/haakon-env/repos/node-tracking/node_modules/hapi-swagger/lib/paths.js:151:17)
    at Object.builder.getSwaggerJSON (/Users/timjones/gyda/haakon-env/repos/node-tracking/node_modules/hapi-swagger/lib/builder.js:109:26)
    at settings.log.plugin.route.config.handler.plugin.methods.getSwaggerJSON.Builder.getSwaggerJSON (/Users/timjones/gyda/haakon-env/repos/node-tracking/node_modules/hapi-swagger/lib/index.js:115:29)
    at Object.exports.execute.internals.prerequisites.internals.handler.callback [as handler] (/Users/timjones/gyda/haakon-env/repos/node-tracking/node_modules/hapi/lib/handler.js:96:36)
    at /Users/timjones/gyda/haakon-env/repos/node-tracking/node_modules/hapi/lib/handler.js:30:23
    at internals.Protect.run.finish [as run] (/Users/timjones/gyda/haakon-env/repos/node-tracking/node_modules/hapi/lib/protect.js:62:12)
    at exports.execute.finalize (/Users/timjones/gyda/haakon-env/repos/node-tracking/node_modules/hapi/lib/handler.js:24:22)
    at each (/Users/timjones/gyda/haakon-env/repos/node-tracking/node_modules/hapi/lib/request.js:380:16)
    at iterate (/Users/timjones/gyda/haakon-env/repos/node-tracking/node_modules/hapi/node_modules/items/lib/index.js:36:13)
    at done (/Users/timjones/gyda/haakon-env/repos/node-tracking/node_modules/hapi/node_modules/items/lib/index.js:28:25)
    at /Users/timjones/gyda/haakon-env/repos/node-tracking/node_modules/hapi/lib/route.js:384:20
    at /Users/timjones/gyda/haakon-env/repos/node-tracking/node_modules/hapi/node_modules/statehood/lib/index.js:244:16

What did you expect ?

No error. It looks like properties.parseAlternatives assumes there must be a .then around line 478 of properties.js.

[Y-LyN-10]

Hello! The fix proposed by @hostiphur works, but looks-like that it was commented out at some point, so this issue is reproducible now (with Joi.forbidden() )

hapi: v17.4.0 hapi-swagger: v9.1.1 joi: v13.1.2

[zsiglin]

@glennjones Can we get this reimplemented? Any reason this was commented out?