code: public function requireParam($key)
      {
          $param = $this->fetch($key, function ($key) {
              throw new ParameterMissingException("Missing param '$key'");
          });
  
          if ($this->valueIsEmpty($param)) {
              throw new ParameterMissingException("Missing param '$key'");
          }
  
          return $param;
      }
docs: Makes sure a parameter was passed
  
  @param  string                    $key the parameter key
  @return Parameters
  @throws ParameterMissingException when parameter is missing