It's normal. I get why you don't want to tell them your current salary but why not tell the expectations? It's a waste of time for you and the company if they can't offer what you think you deserve for that job. In any case, you can say your expectation salary and tell them you are flexible with other offer if it's reasonable for the tasks to be done. Before to give a estimate salary, do some research about how much it's a reasonable salary for the amount of task of the job and see if you need more or not.