Q: How to do a comparative discussion of results if no previous work on the topic exists?

It is a good thing that your research idea is original and no one has actually applied it before. In fact, you should be glad that your research is so novel. However, you need to conduct a literature search once again using different combinations of keywords to make sure that there is actually no existing literature on the topic. Even after doing this if you find nothing on the same research idea or the same topic, you can compare your research with research that has been done on closely related topics. Another approach would be to go a little broader and compare it with other studies in the same subject area, if not on the specific topic. Perhaps you can add a sentence saying that while a lot of studies have focused on various aspects of the topic or subject area, none of them deal with this particular research idea.