TabularForm doesn't play well with INPUT_FILE

[skills-up]

Prerequisites

• [x] I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• [x] The issue still exists against the latest master branch of yii2-builder.
• [x] This is not an usage question. I confirm having gone through and read the documentation and demo.
• [x] This is not a general programming / coding question. (Those should be directed to the webtips Q & A forum).
• [x] I have attempted to find the simplest possible steps to reproduce the issue.
• [ ] I have included a failing test as a pull request (Optional).

Steps to reproduce the issue

1. Add a INPUT_FILE field type in a TabularForm widget, for related models.
2. Open the form in browser.
3. You will see a javascript error.

Expected behavior and actual behavior

When I follow those steps, I see...

Uncaught TypeError: self.previewCache.data.content.filter is not a function
    at Object.fetch (fileinput.js:608)
    at Object.count (fileinput.js:614)
    at FileInput._initPreview (fileinput.js:1171)
    at FileInput._init (fileinput.js:329)
    at new FileInput (fileinput.js:239)
    at HTMLInputElement.<anonymous> (fileinput.js:3417)
    at Function.each (jquery.js:365)
    at jQuery.fn.init.each (jquery.js:137)
    at jQuery.fn.init.$.fn.fileinput (fileinput.js:3405)
    at HTMLDocument.<anonymous> (update?client=ChrysCapital+VI.+LLC&traveller_name=Test+Traveller:1218)

I was expecting... The file input to work correctly. I think a part of the problem may be absence of enctype attribute for the tabular form (at least it is not documented anywhere if it is present).

Environment

PHP v5.6.28 on Mac OS X 10.12 using MAMP server

Browsers

• [x] Google Chrome
• [ ] Mozilla Firefox
• [ ] Internet Explorer
• [x] Safari

Operating System

• [ ] Windows
• [x] Mac OS X
• [ ] Linux
• [ ] Mobile

Libraries

• jQuery version:
• yii2-builder version:

Isolating the problem

• [ ] This bug happens on the demos page
• [x] The bug happens consistently across all tested browsers
• [ ] This bug happens when using yii2-builder without other plugins.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.