Fix model generator

[jannyHou]

A fix to strongloop/loopback#2292 (comment)

Model generator is broken due to the name check of property:

`? Enter the model name: Contact
? Select the data-source to attach undefined to: db (memory)
? Select model's base class PersistedModel
? Expose Contact via the REST API? Yes
? Custom plural form (used to build REST URL): 
? Common model or server only? common
Let's add some Contact properties now.

Enter an empty property name when done.
? Property name: 
>> Name cannot contain special characters [object Object]email
`

If we use
[validate: validateOptionalName](https://github.com/strongloop/generator-loopback/blob/master/model/index.js#L224) to validate name, it will provide a second argument to the function validateOptionalName`:
use console.log to show it

JSON.stringify(second arg): {}
second arg: [object Object]

So it refuse name that match [object Object]
.

Use

validate: function(value) {
  validateOptionalName(value);
}

instead to fix it by forcing the second argument as undefined.

[jannyHou]

Our test case unable to cover mocking the property test in a model generator.
So I manually verify it on my local:

1. reinstall your generator-loopback
2. apply this fix into your generator-loopback code: https://github.com/strongloop/generator-loopback/pull/194/files
3. Try slc loopback:model and after input model info, name a property as email

@bajtos Please review, thanks!

[bajtos]

This change looks rather puzzling to me. What is the underlying problem? Is inquirer providing more than one argument to validate? Please check all other places that are calling validateOptionalName, actually any of the validate* methods to verify they are not subject to the same issue.

Also please put more details in the commit message to explain what you are actually fixing and why.

[jannyHou]

@bajtos Sure I will take a look of other places. I find the solution by chance and it's puzzling to me too.

inquirer providing more than one argument to validate

i also suspect it.

[raymondfeng]

It seems that yeoman validate is now called with two args (value and answers). See https://github.com/SBoudrias/Inquirer.js/blob/master/lib/prompts/base.js#L89

[raymondfeng]

I wonder if it's better to fix https://github.com/strongloop/generator-loopback/blob/master/lib/helpers.js#L104.

[jannyHou]

Closing it since #195 merged 👍