Unable to disable Recursive search in Advanced Search Block

[kylehuynh205]

How to reproduce

• Add a Advanced Search Form Block, Select an option of Context Filter:
  

• Save the block

• Open the block configuration again, try to unselect the selected option in Context Filter dropdown, but it's impossible to do that

Diagnosis

• To be able to unselect the Context filter, change "#multiple => TRUE" at this line, However, the Advanced Search block is not rendered because of this error:

TypeError: Drupal\advanced_search\Form\AdvancedSearchForm::buildForm(): Argument #6 ($context_filter) must be of type ?string, array given in Drupal\advanced_search\Form\AdvancedSearchForm->buildForm() (line 254 of /var/www/D10-doris/web/modules/contrib/advanced_search/src/Form/AdvancedSearchForm.php)
#0 [internal function]: Drupal\advanced_search\Form\AdvancedSearchForm->buildForm()
#1 /var/www/D10-doris/web/core/lib/Drupal/Core/Form/FormBuilder.php(536): call_user_func_array()
#2 /var/www/D10-doris/web/core/lib/Drupal/Core/Form/FormBuilder.php(283): Drupal\Core\Form\FormBuilder->retrieveForm()
#3 /var/www/D10-doris/web/core/lib/Drupal/Core/Form/FormBuilder.php(224): Drupal\Core\Form\FormBuilder->buildForm()
#4 /var/www/D10-doris/web/modules/contrib/advanced_search/src/Plugin/Block/AdvancedSearchBlock.php(377): Drupal\Core\Form\FormBuilder->getForm()
#5 /var/www/D10-doris/web/core/modules/block/src/BlockViewBuilder.php(171): Drupal\advanced_search\Plugin\Block\AdvancedSearchBlock->build()
#6 [internal function]: Drupal\block\BlockViewBuilder::preRender()
#7 /var/www/D10-doris/web/core/lib/Drupal/Core/Security/DoTrustedCallbackTrait.php(111): call_user_func_array()
#8 /var/www/D10-doris/web/core/lib/Drupal/Core/Render/Renderer.php(858): Drupal\Core\Render\Renderer->doTrustedCallback()
#9 /var/www/D10-doris/web/core/lib/Drupal/Core/Render/Renderer.php(421): Drupal\Core\Render\Renderer->doCallback()
#10 /var/www/D10-doris/web/core/lib/Drupal/Core/Render/Renderer.php(240): Drupal\Core\Render\Renderer->doRender()
#11 /var/www/D10-doris/web/core/lib/Drupal/Core/Render/Renderer.php(165): Drupal\Core\Render\Renderer->render()
#12 /var/www/D10-doris/web/core/lib/Drupal/Core/Render/Renderer.php(627): Drupal\Core\Render\Renderer->Drupal\Core\Render\{closure}()
#13 /var/www/D10-doris/web/core/lib/Drupal/Core/Render/Renderer.php(166): Drupal\Core\Render\Renderer->executeInRenderContext()
#14 /var/www/D10-doris/web/core/lib/Drupal/Core/Render/Renderer.php(183): Drupal\Core\Render\Renderer->renderPlain()
#15 /var/www/D10-doris/web/core/lib/Drupal/Core/Render/Renderer.php(220): Drupal\Core\Render\Renderer->doRenderPlaceholder()
#16 /var/www/D10-doris/web/core/modules/big_pipe/src/Render/BigPipe.php(723): Drupal\Core\Render\Renderer->renderPlaceholder()
#17 /var/www/D10-doris/web/core/modules/big_pipe/src/Render/BigPipe.php(554): Drupal\big_pipe\Render\BigPipe->renderPlaceholder()
#18 [internal function]: Drupal\big_pipe\Render\BigPipe->Drupal\big_pipe\Render\{closure}()
#19 /var/www/D10-doris/web/core/modules/big_pipe/src/Render/BigPipe.php(566): Fiber->start()
#20 /var/www/D10-doris/web/core/modules/big_pipe/src/Render/BigPipe.php(305): Drupal\big_pipe\Render\BigPipe->sendPlaceholders()
#21 /var/www/D10-doris/web/core/modules/big_pipe/src/Render/BigPipeResponse.php(112): Drupal\big_pipe\Render\BigPipe->sendContent()
#22 /var/www/D10-doris/vendor/symfony/http-foundation/Response.php(425): Drupal\big_pipe\Render\BigPipeResponse->sendContent()
#23 /var/www/D10-doris/web/index.php(20): Symfony\Component\HttpFoundation\Response->send()
#24 {main}

• the Context Filter of Advanced Search block is saved as as array context_filter: {} instead of string:

uuid: b5911555-37bb-4eef-9d36-4db5b4d54a91
langcode: en
status: true
dependencies:
  module:
    - advanced_search
    - term_condition
  theme:
    - barriodepartments
id: barriodepartments_advancedsearchforcollectionmembers
theme: barriodepartments
region: sidebar_first
weight: -11
provider: null
plugin: 'advanced_search_block:advanced_search__block_1'
settings:
  id: 'advanced_search_block:advanced_search__block_1'
  label: 'Advanced Search: Advanced Search for Collection Members'
  label_display: '0'
  provider: advanced_search
  fields:
    - fulltext_title
    - field_description
    - genre_full_text
    - subject_full_text
    - field_edtf_date_created
  context_filter: {}
visibility:
  term:
    id: term
    negate: false
    context_mapping: {  }
    term_uuids:
      - 6d559ff0-ebbb-4338-a47c-cbec82e822bb

[gerbie-goober]

PR made to disable subcollection search: #7