By the definitions, the null hypothesis is always, or includes, no difference. It is also the general rule that you never accept the null, you can just fail to reject it. That makes hypothesizing to fail to reject the null a bit odd as well.

Has anyone come across a similar situation and had to phrase the question in terms of null and alternative hypotheses? In practical research one would just write that they expect no difference, run the test (with significant power to find a difference) and if no significant difference was found then say that.