How to link a modifiable simple collection with an attribute in the database?

Hi all,

In my UI I would like to create a list of stats (mean, min, max) so the user can remove them or add a customize stat. I followed this Bonita documentation to create a modifiable simple collection:

https://documentation.bonitasoft.com/bonita/7.11/repeat-a-container-for-...

What I have is:

• A business model called TestChecklist with an attribute named checklist (multiple string).
• In the UI I create a JSON variable named stats_lists with the flowing array: ["p75", "mean", "min", "max"]
• In the UI there is a container which has stats_list in the Collection. Inside this container there is an input and a button widget. The input has a value of $item and the button has a Remove from collection Action, a Collection value of $collection, a Remove Item and an $item in Item to remove.
• Outside the previous container there is another button with an Add to collection Action, the stats_list as Collection and Last in Add.
• The formOutput looks like:
  if( $data.testChecklist ){
  return {
  //map testChecklist variable to expected task contract input
  testChecklistInput: {
  checklist: $data.testChecklist.checklist !== undefined ? $data.testChecklist.checklist : null
  }
  }
  }
• When I try to submit the process I get the following error:
  Debug message
  Error while validating expected inputs
  Expected input [testChecklistInput] is missing

How can I link the result of the stats list to my attribute checklist?

Thanks in advance!