Date Widget Property Gets Removed if value is 'blank' - ( For Widget Nested Inside an Object )

[ghost]

- Do you want to request a feature or report a bug?
Bug
- What is the current behavior?
In this code,

- name: "pre-ico"
  label: "Pre ICO Information"
  widget: object
  fields:
   - label: "Pre ICO Start Date"
     name: "start-date"
     widget: "date"
     default: ""
     format: "MMM-DD-YYYY"
   - label: "Pre ICO End Date"
     name: "end-date"
     widget: "date"
     default: ""
     format: "MMM-DD-YYYY"

Instead of returning
start-date: ''
the start date property is removed from the file if left blank while saving
strangely though the end date property gets saved correctly as
end-date: ''

- If the current behavior is a bug, please provide the steps to reproduce.
Please use the above configuration code and set date fields to blank to reproduce the issue
- What is the expected behavior?
blank date fields set properly as
start-date: ''
end-date: ''

- Please mention your versions where applicable.

1.5

Netlify CMS version:
Browser version:

Node.JS version:
Operating System:

- Please link or paste your config.yml below if applicable.

[tech4him1]

Possibly related to #1117.

[barthc]

@erquhart can we now close this?