code: protected function setCacheState($useCache)
      {
          if (is_bool($useCache)) {
              $this->useCache = $useCache;
          } else {
              // every invalid param would activate cache
              $this->useCache = true;
          }
      }
docs: Sets value if cache should be used or not
  
  @param boolean $useCache the cache state
  
  @return void