code: def filter_merged_pull_requests(self, pull_requests):
          
  
          if self.options.verbose:
              print("Fetching merge date for pull requests...")
          closed_pull_requests = self.fetcher.fetch_closed_pull_requests()
  
          if not pull_requests:
              return []
          pulls = copy.deepcopy(pull_requests)
          for pr in pulls:
              fetched_pr = None
              for fpr in closed_pull_requests:
                  if fpr['number'] == pr['number']:
                      fetched_pr = fpr
              if fetched_pr:
                  pr['merged_at'] = fetched_pr['merged_at']
                  closed_pull_requests.remove(fetched_pr)
  
          for pr in pulls:
              if not pr.get('merged_at'):
                  pulls.remove(pr)
          return pulls
docs: This method filter only merged PR and fetch missing required
          attributes for pull requests. Using merged date is more correct
          than closed date.
  
          :param list(dict) pull_requests: Pre-filtered pull requests.
          :rtype: list(dict)
          :return: