Many inverter manufacturers won't add a DC breaker/DC switch in their inverters in order to keep it at a low cost. Anyway, without a breaker, it is not a big deal for power inverters as it is still functional.
However, under safety considerations, it should come with a DC breaker.
For example, when it should connect with positive "+" to positive "+", some people connect it with positive "+" to negative "-", the inverter is likely to be spoiled instantly. However, if it comes with a DC breaker, you have time to check and revise it properly.