Is it common for a thesis-based master hasn't got the thesis topic?
This can happen. The formal thesis topic is quite an open field.

Perhaps, the supervisor doesn't want to spoon-feed and force a topic on to you, but rather would want to have you come up with one. By exposing you to various tools and techniques, and (presumably) side-by-side pointing to some useful literature, and asking you to dig for more works yourself, he/she is essentially doing a good job. Basically, what he's saying is - this is what happens usually in the field, tell me if you come up with any ideas regarding what you want to do. He/she is basically throwing the field open to you.

Since your master's is thesis based, I won't find it very surprising though if he/she has already planned something as a backup option, in case you don't come up with anything reasonable. But he/she will likely not reveal that unless he/she is absolutely convinced that you are struggling to come up with anything doable.

In my experience, this approach is not very common, but not very rare either. And of course, it is a good approach, the goal of course is to train you to think.

Hope that helps. :)