Quick Open hover shows 'null'

[gregvanl]

• VSCode Version: 1.29 Insiders
• OS Version: Windows 10

Steps to Reproduce:

1. Bring up Quick Open (workbench.action.quickOpen)
2. Hover over a list item

You see a hover (don't see this in 1.28) with the text 'null'.

Does this issue occur when all extensions are disabled?: Yes/No

[gregvanl]

Also repro's in the Command Palette

[bpasero]

@isidorn maybe a change in IconLabel / ResourceLabel? Also ping @jrieken

[jrieken]

maybe a strict null issue? the highlight label can optional (undefined) take a title attribute and I can image that this has become null somewhere down the path

[gpoussel]

This is due to 318250a I guess.

[isidorn]

@gpoussel thanks for the PR, assigned it to @sandy081 to review since it is his commit

[isidorn]

I verified that the PR does indeed fix the issue. Once @sandy081 gives the thumbs up, we can merge it in

[sandy081]

Pushed the PR.

Thanks @gpoussel