Validation Scenario for required but not rendered fields: Uncaught TypeError: [tcomb] Invalid value undefined supplied to Struct

Version

Tell us which versions you are using:

tcomb-form v0.9.10?
tcomb v3.2.15
react v15.4.2?

Expected behaviour

Tell us what should happen

When any given field is marked mandatory/required but not rendered and if valid VALUE exist in context then there shouldn't be a validation error.

Actual behaviour

Tell us what happens instead

const ftype = t.struct({
    YesNo: t.Boolean,
    FirstName: t.String,
    LastName: t.String
})

var value = {
YesNo: false,
FirstName: "Jhon",
LastName: "Smith"
}

In the above simple Form of 3 fields, all are required fields. However, via templates when one of the fields are not rendered for given condition (let's say if true don't render LastName) and form only has the Checkbox and FirstName. When refs.form.validate() is triggered I get below error despite my value object having LastName value.

Uncaught TypeError: [tcomb] Invalid value undefined supplied to Struct{YesNo: String, FirstName: String, LastName: String}/LastName: String

No Error when LastName is made optional by t.maybe()

const ftype = t.struct({
    YesNo: t.Boolean,
    FirstName: t.String,
    LastName: t.maybe(t.String)
})

Also, No Error when LastName is displayed in form and obviously the value is populated to the field and validation passes through.

Steps to reproduce

Create a simple form with required fields
Have valid values of respective types
Use template to control whether to render a field or not, let's say don't render the field
On some action (button click) call this.refs.form.validate() -> Uncaught TypeError

Stack trace and console log

Uncaught TypeError: [tcomb] Invalid value undefined supplied to Struct{YesNo: String, FirstName: String, LastName: String}/LastName: String
    at Function.fail (fail.js:2)
    at assert (assert.js:14)
    at Irreducible (irreducible.js:18)
    at create (create.js:9)
    at new Struct (struct.js:82)
    at Struct.validate (components.js:661)
    at Form.validate (components.js:984)
    at ValidationForm._this.onConfirm (ValidationForm.jsx:50)
    at Button._this.handleClick (button.js:100)
    at Object.ReactErrorUtils.invokeGuardedCallback (ReactErrorUtils.js:70)

validation_error_1 validation_error_2 validation_error_4 validation_error_3

Thanks

gcanti / tcomb-form