Elements collection inside class with @Frame annotation isn't working

Method `Elements.getListElement(WebElement el)` clears up parent property in `el` by setting it to `null`.
That's why the `@Frame` information is lost in the context if there was one, and there is no call to the `GetElementModule.getFrameContext(By frame)` method.
As a result all elements in declared Elements collection inside iframe class with @Frame annotation couldn't be found in **DOM**.
Parent property should be saved for all elements inside iframe, because it's necessary to switch into frame to work with internal elements using Selenium.