docs: private Pattern loadAcceptPattern(ExternalContext context)
      {
          assert context != null;
  
          String mappings = context.getInitParameter(ViewHandler.FACELETS_VIEW_MAPPINGS_PARAM_NAME);
          if (mappings == null)
          {
              return null;
          }
  
          // Make sure the mappings contain something
          mappings = mappings.trim();
          if (mappings.length() == 0)
          {
              return null;
          }
  
          return Pattern.compile(toRegex(mappings));
      }