docs: def _collect_settings(self, apps):
          """
          Iterate over given apps or INSTALLED_APPS and collect the content of each's
          settings file, which is expected to be in JSON format.
          """
          contents = {}
          if apps:
              for app in apps:
                  if app not in settings.INSTALLED_APPS:
                      raise CommandError("Application '{0}' not in settings.INSTALLED_APPS".format(app))
          else:
              apps = settings.INSTALLED_APPS
          for app in apps:
              module = import_module(app)
              for module_dir in module.__path__:
                  json_file = os.path.abspath(os.path.join(module_dir, self.json_file))
                  if os.path.isfile(json_file):
                      with open(json_file, 'r') as fp:
                          contents[app] = json.load(fp)
          return contents