Net Debt to Equity or Debt to Equity

I’m a currently in a finance class working on a case where we have to find the unlevered betas of firms in an industry in order to find the WACC of a private firm which we are valuing.

In class our professor used Net Debt to Equity when unlevering Beta instead of Debt to Equity. I asked a question about this but he said was somewhat confident in his stance. As a student I obviously just took his word for it but I’d like to hear more explanation.

Is there any situation in which you’d use net debt to equity instead of debt to equity to unlever beta? I was under the impression that cash was represented in equity value so subtracting it from debt would be double counting the cash.