I receive the above error when sending an attachment with Views Send.
I'm using Mail System with "Mime Mail mailer" for the Formatter and "SMTP Mailer" for the Sender.
The following errors are reported in dblog with the referrer being /batch?id=1794&op=start
Warning: preg_match() expects parameter 2 to be string, object given in Drupal\Core\File\FileSystem->uriScheme() (line 293 of /vagrant/docroot/core/lib/Drupal/Core/File/FileSystem.php) #0 /vagrant/docroot/core/includes/bootstrap.inc(587): _drupal_error_handler_real(2, 'preg_match() ex...', '/vagrant/docroo...', 293, Array) #1 [internal function]: _drupal_error_handler(2, 'preg_match() ex...', '/vagrant/docroo...', 293, Array) #2 /vagrant/docroot/core/lib/Drupal/Core/File/FileSystem.php(293): preg_match('/^([\\w\\-]+):\\/\\...', Object(Drupal\Core\Field\FieldItemList), NULL) #3 /vagrant/docroot/core/includes/file.inc(107): Drupal\Core\File\FileSystem->uriScheme(Object(Drupal\Core\Field\FieldItemList)) #4 /vagrant/docroot/core/lib/Drupal/Core/StreamWrapper/StreamWrapperManager.php(103): file_uri_scheme(Object(Drupal\Core\Field\FieldItemList)) #5 /vagrant/docroot/core/lib/Drupal/Core/File/FileSystem.php(132): Drupal\Core\StreamWrapper\StreamWrapperManager->getViaUri(Object(Drupal\Core\Field\FieldItemList)) #6 /vagrant/docroot/modules/contrib/smtp/src/Plugin/Mail/SMTPMailSystem.php(431): Drupal\Core\File\FileSystem->realpath(Object(Drupal\Core\Field\FieldItemList)) #7 /vagrant/docroot/modules/contrib/mailsystem/src/Adapter.php(50): Drupal\smtp\Plugin\Mail\SMTPMailSystem->mail(Array) #8 /vagrant/docroot/modules/contrib/views_send/views_send.module(850): Drupal\mailsystem\Adapter->mail(Array) #9 /vagrant/docroot/modules/contrib/views_send/views_send.module(858): views_send_deliver(Object(stdClass)) #10 /vagrant/docroot/core/includes/batch.inc(295): views_send_batch_deliver(Array, false, Array, Array) #11 /vagrant/docroot/core/includes/batch.inc(137): _batch_process() #12 /vagrant/docroot/core/includes/batch.inc(93): _batch_do() #13 /vagrant/docroot/core/modules/system/src/Controller/BatchController.php(55): _batch_page(Object(Symfony\Component\HttpFoundation\Request)) #14 [internal function]: Drupal\system\Controller\BatchController->batchPage(Object(Symfony\Component\HttpFoundation\Request)) #15 /vagrant/docroot/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(123): call_user_func_array(Array, Array) #16 /vagrant/docroot/core/lib/Drupal/Core/Render/Renderer.php(582): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() #17 /vagrant/docroot/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(124): Drupal\Core\Render\Renderer->executeInRenderContext(Object(Drupal\Core\Render\RenderContext), Object(Closure)) #18 /vagrant/docroot/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(97): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) #19 /vagrant/vendor/symfony/http-kernel/HttpKernel.php(151): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() #20 /vagrant/vendor/symfony/http-kernel/HttpKernel.php(68): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1) #21 /vagrant/docroot/core/lib/Drupal/Core/StackMiddleware/Session.php(57): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #22 /vagrant/docroot/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(47): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #23 /vagrant/docroot/core/modules/page_cache/src/StackMiddleware/PageCache.php(106): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #24 /vagrant/docroot/core/modules/page_cache/src/StackMiddleware/PageCache.php(85): Drupal\page_cache\StackMiddleware\PageCache->pass(Object(Symfony\Component\HttpFoundation\Request), 1, true) #25 /vagrant/docroot/modules/contrib/shield/src/ShieldMiddleware.php(84): Drupal\page_cache\StackMiddleware\PageCache->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #26 /vagrant/docroot/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(47): Drupal\shield\ShieldMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #27 /vagrant/docroot/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(52): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #28 /vagrant/vendor/stack/builder/src/Stack/StackedHttpKernel.php(23): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #29 /vagrant/docroot/core/lib/Drupal/Core/DrupalKernel.php(693): Stack\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #30 /vagrant/docroot/index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request)) #31 {main}.
Warning: realpath() expects parameter 1 to be a valid path, object given in Drupal\Core\File\FileSystem->realpath() (line 136 of /vagrant/docroot/core/lib/Drupal/Core/File/FileSystem.php) #0 /vagrant/docroot/core/includes/bootstrap.inc(587): _drupal_error_handler_real(2, 'realpath() expe...', '/vagrant/docroo...', 136, Array) #1 [internal function]: _drupal_error_handler(2, 'realpath() expe...', '/vagrant/docroo...', 136, Array) #2 /vagrant/docroot/core/lib/Drupal/Core/File/FileSystem.php(136): realpath(Object(Drupal\Core\Field\FieldItemList)) #3 /vagrant/docroot/modules/contrib/smtp/src/Plugin/Mail/SMTPMailSystem.php(431): Drupal\Core\File\FileSystem->realpath(Object(Drupal\Core\Field\FieldItemList)) #4 /vagrant/docroot/modules/contrib/mailsystem/src/Adapter.php(50): Drupal\smtp\Plugin\Mail\SMTPMailSystem->mail(Array) #5 /vagrant/docroot/modules/contrib/views_send/views_send.module(850): Drupal\mailsystem\Adapter->mail(Array) #6 /vagrant/docroot/modules/contrib/views_send/views_send.module(858): views_send_deliver(Object(stdClass)) #7 /vagrant/docroot/core/includes/batch.inc(295): views_send_batch_deliver(Array, false, Array, Array) #8 /vagrant/docroot/core/includes/batch.inc(137): _batch_process() #9 /vagrant/docroot/core/includes/batch.inc(93): _batch_do() #10 /vagrant/docroot/core/modules/system/src/Controller/BatchController.php(55): _batch_page(Object(Symfony\Component\HttpFoundation\Request)) #11 [internal function]: Drupal\system\Controller\BatchController->batchPage(Object(Symfony\Component\HttpFoundation\Request)) #12 /vagrant/docroot/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(123): call_user_func_array(Array, Array) #13 /vagrant/docroot/core/lib/Drupal/Core/Render/Renderer.php(582): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() #14 /vagrant/docroot/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(124): Drupal\Core\Render\Renderer->executeInRenderContext(Object(Drupal\Core\Render\RenderContext), Object(Closure)) #15 /vagrant/docroot/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(97): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) #16 /vagrant/vendor/symfony/http-kernel/HttpKernel.php(151): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() #17 /vagrant/vendor/symfony/http-kernel/HttpKernel.php(68): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1) #18 /vagrant/docroot/core/lib/Drupal/Core/StackMiddleware/Session.php(57): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #19 /vagrant/docroot/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(47): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #20 /vagrant/docroot/core/modules/page_cache/src/StackMiddleware/PageCache.php(106): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #21 /vagrant/docroot/core/modules/page_cache/src/StackMiddleware/PageCache.php(85): Drupal\page_cache\StackMiddleware\PageCache->pass(Object(Symfony\Component\HttpFoundation\Request), 1, true) #22 /vagrant/docroot/modules/contrib/shield/src/ShieldMiddleware.php(84): Drupal\page_cache\StackMiddleware\PageCache->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #23 /vagrant/docroot/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(47): Drupal\shield\ShieldMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #24 /vagrant/docroot/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(52): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #25 /vagrant/vendor/stack/builder/src/Stack/StackedHttpKernel.php(23): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #26 /vagrant/docroot/core/lib/Drupal/Core/DrupalKernel.php(693): Stack\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #27 /vagrant/docroot/index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request)) #28 {main}.
The email is successfully sent without any attachments.
The file is successfully uploaded and placed in the subfolder "views_send_attachments" and remains there.