code: public ExtensionIssueManagement getExtensionIssueManagement(String system, String url)
      {
          return getExtensionIssueManagement(new DefaultExtensionIssueManagement(system, url));
      }
docs: Store and return a weak reference equals to the passed {@link ExtensionIssueManagement} elements.
  
  @param system the name of the issue management system (jira, bugzilla, etc.)
  @param url the URL of that extension in the issues management system
  @return unique instance of {@link ExtensionIssueManagement} equals to the passed one