Named route records with multiple optional params result in empty URL when param is unused and path does not have trailing slash

[gryphonmyers]

Version

4.1.2

Reproduction link

jsfiddle.net/98gw1b3p/

Steps to reproduce

1. Create a named route with a path containing two optional params one after the other, with a trailing slash
2. Create a router link that links to this route by name using a route object and no params
3. Observe that the router link href links to "/"
4. Create a named route with a path containing two optional params one after the other, with no trailing slash
5. Create a router link that links to this route by name using a route object and no params
6. Observe that the router link has no href

What is expected?

When no params are supplied to a named route with two or more optional params, the rendered router-link should have an href attribute of "/" regardless of whether a trailing slash is used or not.

What is actually happening?

When no params are supplied to a named route with two or more optional params, the rendered router-link has an href of "/" if the route path has a trailing slash, but has no href if no trailing slash is used.

[gryphonmyers]

Related to #1357