Why ChromeRenderFrameObserver::ShouldCapturePageTextForTranslateOrPhishing check render_frame()->GetWebFrame() is Null

[wd l]

I am studying the chromium source code. Today I found a strange problem. Why do We need to determine that render_frame()->GetWebFrame() is not empty in ChromeRenderFrameObserver::ShouldCapturePageTextForTranslateOrPhishing[1]?

[1] https://source.chromium.org/chromium/chromium/src/+/main:chrome/renderer/chrome_render_frame_observer.cc;l=579;bpv=0;bpt=1