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 seems the smart money knows that debt – which is usually involved in bankruptcies – is a very important factor, when you assess how risky a company is. We can see that AECOM (NYSE:ACM) does use debt in its business. But the real question is whether…