code: String getRequiredInitParameter(String name) throws ServletException {
          String value = getInitParameter(name);
          if (value == null) {
              throw new ServletException(MessageFormat.format(nls.getString("Missing.required.initialization.parameter","Missing required initialization parameter: {0}"), new Object[]{name}));
          }
  
          return value;
      }
docs: Retrieve a required init parameter by name.
  @exception javax.servlet.ServletException thrown if the required parameter is not present.