Proposal: unmatched optional path segments produce undefined prop values

[developit]

Currently, optional path segments that do not match a current URL produce same-named props with an empty string value:

exec('/posts', '/posts/:user?/:id?', {})
// { user: "", id: "" }

exec('/posts/bob', '/posts/:user?/:id?', {})
// { user: "bob", id: "" }

With this PR, the value for optional path segments that have no match is an empty string. Matched path segments that are empty will still produce an empty string.

exec('/posts', '/posts/:user?/:id?', {})
// { user: undefined, id: undefined }

exec('/posts/bob', '/posts/:user?/:id?', {})
// { user: "bob", id: undefined }

This is a major change, because it means any defaultProps for route components will be applied for empty/missing route parameters - currently they are not.

Fixes #381.

ToDo

• [ ] update tests