code: protected function grabParameter(ReflectionParameter $parameter)
      {
          if (isset($this->values[$parameter->name]))
          {
              return $this->values[$parameter->name];
          }
  
          if ($parameter->isDefaultValueAvailable())
          {
              return $parameter->getDefaultValue();
          }
  
          throw new Exception("Unable to map parameter [{$parameter->name}] to command [{$this->command}]");
      }
docs: Get a parameter value for a marshaled command.
  
  @author	Andrea Marco Sartori
  @param  \ReflectionParameter  $parameter
  @return mixed