[MdDatepicker] Multiple Vue Warn Messages

[sl-digital]

Steps to reproduce

using "vue-material" : "1.0.0-beta-7"

1. Import and use MdDatepicker with defaults in Vue template.
2. Build in Webpack and load page.
3. On click MdDatepicker opens with multiple console errors

Which browser?

All browsers tested except Firefox where the Datepicker defaults to the system.

What is expected?

No console errors.

What is actually happening?

[Vue warn]: Invalid prop: type check failed for prop "mdDate". Expected Date, got String.
[Vue warn]: Duplicate keys detected: '1'. This may cause an update error.

[Samuell1]

1. Dont use string use null as empty value.
2. Duplicate of [MdDatepicker] Error on open #1376

[sl-digital]

Where is the fix from #1376?

[Samuell1]

@sl-digital in dev branch