Add Exception When Unable to load module from extensions. (#4252)

* Throws exception when unable to load module extension for module
generator.

* Simplifies code line.

Co-authored-by: Nikolay Lobachev <nikolay.lobachev@gmail.com>

Author: johnbburg

src/Generator/ComposerGenerator.php

@@ -40,10 +40,14 @@ public function __construct(
     public function generate(array $parameters)
     {
         $machineName = $parameters['machine_name'];
+        $module = $this->extensionManager->getModule($machineName);
+        if (!$module) {
+          throw new \Exception(
+          "Unable to load module: \"{$machineName}\" from extension manager. This may be an unresolved issue in the module generator. This will prevent the generator from creating the composer.json file for the module. Try calling the command without setting dependencies. See https://github.com/hechoendrupal/drupal-console/issues/4118");
+        }
         $composerPath = !is_null($parameters['package_path']) ?
           $parameters['package_path'] . '/' . $machineName . '/composer.json' :
-          $this->extensionManager->getModule($machineName)
-            ->getPath() . '/composer.json';
+          $module->getPath() . '/composer.json';
         $this->renderFile(
           'module/composer.json.twig',
           $composerPath,