The external fund manager backed by Berkshire Hathaway’s Charlie Munger, Li Lu, makes no bones about it when he says ‘The biggest investment risk is not the volatility of prices, but whether you will suffer a permanent loss of capital.’ So it might be obvious that you need to consider debt, when you think about how risky any given stock is, because too much debt can sink a company. We can see that Generac Holdings Inc. (NYSE:GNRC) does use debt in its business. But should shareholders be…