null converted to empty array needed single quotes

While extending the Lightning module via the provided lightning.extend.yml adding null as a dependency caused the following error on install.

exception 'Drupal\Core\Extension\MissingDependencyException' with message 'Unable to install modules Array, 1,  due to missing modules Array, 1, .' in                    [error]
/var/www/docroot/core/lib/Drupal/Core/Extension/ModuleInstaller.php:85
Stack trace:
#0 /var/www/docroot/core/lib/Drupal/Core/ProxyClass/Extension/ModuleInstaller.php(83): Drupal\Core\Extension\ModuleInstaller->install(Array, true)
#1 /var/www/docroot/profiles/contrib/lightning/lightning.profile(62): Drupal\Core\ProxyClass\Extension\ModuleInstaller->install(Array)
#2 [internal function]: lightning_install_module(Array)
#3 /var/www/docroot/core/includes/batch.inc(252): call_user_func_array('lightning_insta...', Array)
#4 /var/www/docroot/core/includes/form.inc(870): _batch_process()
#5 /var/www/docroot/core/includes/install.core.inc(615): batch_process(Object(Drupal\Core\Url), Object(Drupal\Core\Url))
#6 /var/www/docroot/core/includes/install.core.inc(536): install_run_task(Array, Array)
#7 /var/www/docroot/core/includes/install.core.inc(115): install_run_tasks(Array)
#8 phar:///usr/local/bin/drush/includes/drush.inc(726): install_drupal(Object(Composer\Autoload\ClassLoader), Array)
#9 phar:///usr/local/bin/drush/includes/drush.inc(711): drush_call_user_func_array('install_drupal', Array)
#10 phar:///usr/local/bin/drush/commands/core/drupal/site_install.inc(80): drush_op('install_drupal', Object(Composer\Autoload\ClassLoader), Array)
#11 phar:///usr/local/bin/drush/commands/core/site_install.drush.inc(247): drush_core_site_install_version(NULL, Array)
#12 [internal function]: drush_core_site_install()
#13 phar:///usr/local/bin/drush/includes/command.inc(366): call_user_func_array('drush_core_site...', Array)
#14 phar:///usr/local/bin/drush/includes/command.inc(217): _drush_invoke_hooks(Array, Array)
#15 [internal function]: drush_command()
#16 phar:///usr/local/bin/drush/includes/command.inc(185): call_user_func_array('drush_command', Array)
#17 phar:///usr/local/bin/drush/lib/Drush/Boot/BaseBoot.php(67): drush_dispatch(Array)
#18 phar:///usr/local/bin/drush/includes/preflight.inc(66): Drush\Boot\BaseBoot->bootstrap_and_dispatch()
#19 phar:///usr/local/bin/drush/includes/startup.inc(321): drush_main()
#20 phar:///usr/local/bin/drush/drush(114): drush_startup(Array)
#21 /usr/local/bin/drush(10): require('phar:///usr/loc...')
#22 {main}

Adding null in single quotes solved the issue.