Fixed problem with associated_products not visible in backend

[fballiano]

If you create a grouped product, when you associate some products to the grouped and save, they won't appear in the "associated products" tab.

This is because #2715 changed the lines that are reverted in this PR, switching the default value from null to [] and causing a series of other checks to fail.

With this PR the funcionality is working again.

Related Pull Requests

1. Keep current selection for Related, Up-sells, Cross-sells, Associated grids #2715

Fixed Issues (if relevant)

1. Fixes Associated product in admin not visible #3066

Manual testing scenarios (*)

1. create a grouped product
2. associate some other products
3. save
4. associated products are not shown (before the PR)

[kiatng]

Doesn't this "unfix" the bug in issue #2715? How about only change this ->setProductsGrouped($this->getRequest()->getPost('products_grouped', null)); for grouped products?

[fballiano]

i thought about that but all those methods are exactly the same, so I don't know.. it seemed better to have consistency between them no?

[fballiano]

I didn't notice that this PR it's actually a complete revert of #2715

uff

the thing is we can't have the grouped products not working at all.

[fballiano]

@kiatng I've reverted everything except the groupedProducts line, which make grouped products work for me again

[luigifab]

There is a strange thing, without this, if you press reset filter, then all is working fine.

[fballiano]

There is a strange thing, without this, if you press reset filter, then all is working fine.

@luigifab the "reset filter" button calls the "superGroupGridOnly" method which wasn't affected by #2715, that's why it still works :-)

[fballiano]

without this one we can't close 19.5/20.1, grouped products are literally broken

[fballiano]

merged and 20ed