preload problem

Hello, I have checked “Image lazy-loading will delay the loading of non-visible images to allow the browser to optimally load all resources for the “above the fold”-page first.” at Extra tab of plugin.

Now I have following in page source:
<link rel='preload' href='' as='style' />

And Google Chrome Developers Console has following warning:
<link rel=preload> has an invalid href value
Is this expected? What is your suggestion to resolve this issue?
Thank you.

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