code: public void userCompletedAction(final String action, BranchViewHandler.
              IBranchViewEvents callback) {
          userCompletedAction(action, null, callback);
      }
docs: <p>A void call to indicate that the user has performed a specific action and for that to be
  reported to the Branch API.</p>
  
  @param action   A {@link String} value to be passed as an action that the user has carried
  out. For example "registered" or "logged in".
  @param callback instance of {@link BranchViewHandler.IBranchViewEvents} to listen Branch view events