Hi,
I’m trying to create an conditional flexible field. I followed the instructions and can create this fields as long as they are text-fields.
As soon as I try to implement a ‘file’-type field I get an ‘Destination not found’ error. Even though I use destination: "@self".
The problem could be related to  issue 322 but issue 322 is marked as closed.
I tried it both in 1.6.19 and 1.7.0-rc. The Forms-Plugin is version 4.0.1
Here is the yaml-file that reproduces that error (Create a page using this blueprint and try to upload a picture):
title: Title
'@extends':
  type: default
  context: blueprints://pages
form:
  fields:
    tabs:
      fields:
        content:
          unset@: true
        costum:
          ordering@: -10
          type: tab
          title: List-items
          fields:
           header.picture_select:
              type: list
              style: vertical
              label: Liste mit Selektion
              classes: field-selection
              fields:
                .slider:
                  type: fieldset
                  title: Slider images
                  fields:
                    .slider.image1:
                      type: file
                      label: linkes Bild
                      destination: '@self'
                      multiple: false
                      accept: 
                        - 'image/*'