Needs to cope with modules that are missing 'core' attribute

Doesn't appear to be the right fix. It does get rid of the errors, but it changed functionality.

D8.7.7 introduced a new way to specify compatibility. Not only made it the core key optional, it introduced core_version_requirement allowing a pattern. Both keys are optional in D8, both may be available but one must be specified. The new way uses core_version-requirement when available and falls back on core.

The functionality concerned here tests compatibility of a module. Which means it must be adjusted to the new method. Depending on the core version running it should adjust the check. Obviously, core later than 8.7.6 should check core_version_requirement when available.

Receiving the follow errors after patch.

Notice: Undefined index: core in Drupal\easy_install\Form\PurgeConfigurationsForm->buildRow() (line 286 of /public_html/modules/easy_install/src/Form/PurgeConfigurationsForm.php) #0 /public_html/core/includes/bootstrap.inc(596): _drupal_error_handler_real(8, 'Undefined index...', '/...', 286, Array) #1.

Which points to:
// Check the core compatibility.
if ($module->info['core'] != \Drupal::CORE_COMPATIBILITY) {
$compatible = FALSE;
$reasons[] = $this->t('This version is not compatible with Drupal
@core_version and should be replaced.', [
'@core_version' => \Drupal::CORE_COMPATIBILITY,
]);
}

I applied patch from #3 and am also now showing same errors as #6.

Same problem here.

Fixed

Fixed ! thank you all for your contributions !

Receiving the following error from #9

Notice: Undefined index: core in Drupal\easy_install\Form\PurgeConfigurationsForm->buildRow() (line 286 of /home/mysite/public_html/modules/easy_install/src/Form/PurgeConfigurationsForm.php)
#0 /home/mysite/public_html/core/includes/bootstrap.inc(600): _drupal_error_handler_real(8, 'Undefined index...', '/home/mysite/...', 286, Array)
#1 /home/mysite/public_html/modules/easy_install/src/Form/PurgeConfigurationsForm.php(286): _drupal_error_handler(8, 'Undefined index...', '/home/mysite/...', 286, Array)
#2 /home/mysite/public_html/modules/easy_install/src/Form/PurgeConfigurationsForm.php(151): Drupal\easy_install\Form\PurgeConfigurationsForm->buildRow(Array, Object(Drupal\Core\Extension\Extension), 'Drupal')
#3 [internal function]: Drupal\easy_install\Form\PurgeConfigurationsForm->buildForm(Array, Object(Drupal\Core\Form\FormState))
#4 /home/mysite/public_html/core/lib/Drupal/Core/Form/FormBuilder.php(520): call_user_func_array(Array, Array)
#5 /home/mysite/public_html/core/lib/Drupal/Core/Form/FormBuilder.php(277): Drupal\Core\Form\FormBuilder->retrieveForm('system_modules', Object(Drupal\Core\Form\FormState))
#6 /home/mysite/public_html/core/lib/Drupal/Core/Controller/FormController.php(91): Drupal\Core\Form\FormBuilder->buildForm(Object(Drupal\easy_install\Form\PurgeConfigurationsForm), Object(Drupal\Core\Form\FormState))
#7 [internal function]: Drupal\Core\Controller\FormController->getContentResult(Object(Symfony\Component\HttpFoundation\Request), Object(Drupal\Core\Routing\RouteMatch))
#8 /home/mysite/public_html/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(123): call_user_func_array(Array, Array)
#9 /home/mysite/public_html/core/lib/Drupal/Core/Render/Renderer.php(573): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}()
#10 /home/mysite/public_html/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(124): Drupal\Core\Render\Renderer->executeInRenderContext(Object(Drupal\Core\Render\RenderContext), Object(Closure))
#11 /home/mysite/public_html/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(97): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array)
#12 /home/mysite/public_html/vendor/symfony/http-kernel/HttpKernel.php(151): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}()
#13 /home/mysite/public_html/vendor/symfony/http-kernel/HttpKernel.php(68): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1)
#14 /home/mysite/public_html/core/lib/Drupal/Core/StackMiddleware/Session.php(57): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#15 /home/mysite/public_html/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(47): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#16 /home/mysite/public_html/core/modules/page_cache/src/StackMiddleware/PageCache.php(106): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#17 /home/mysite/public_html/core/modules/page_cache/src/StackMiddleware/PageCache.php(85): Drupal\page_cache\StackMiddleware\PageCache->pass(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#18 /home/mysite/public_html/core/modules/ban/src/BanMiddleware.php(50): Drupal\page_cache\StackMiddleware\PageCache->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#19 /home/mysite/public_html/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(47): Drupal\ban\BanMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#20 /home/mysite/public_html/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(52): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#21 /home/mysite/public_html/vendor/stack/builder/src/Stack/StackedHttpKernel.php(23): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#22 /home/mysite/public_html/core/lib/Drupal/Core/DrupalKernel.php(694): Stack\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#23 /home/mysite/public_html/index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request))
#24 {main}

Patch might have not applied, when you apply the patch #9, the line 286 will be changed with another code the error that is showing in line 286 is without applying patch.

Please use latest version of the module, 8.x-10.2.

updated to 8.x-10.2 and all seems well now. Thanks