Number `0` is transferred to `undefined` in the input form and in mutators.

[arteria32]

Hi, I found a bug: 0 is wrong transferred to undefined in the form

Example of spec:

{
  "type": "number",
  "defaultValue":0,
  "viewSpec": {
    "type": "base",
    "layout": "row",
    "layoutTitle": "Age",
    "placeholder": "placeholder text"
  }
}

Screenshot: