あの人には会いたくないです

In the sentence あの人には会いたくないです, what is the function of the は? The sentence makes sense to me without the は but not with it.

Thanks.

The は is used as a contrast marker: "I don't want to meet that person (but I wouldn't mind meeting someone else)." In other words, it's not that you don't feel like meeting anyone - you just don't want to meet that person in particular.

This は often appears in negative sentences (e.g., 私にはできません, 彼には教えません or この金額では買えません) since "someone can't do but others can do/something can't be done but other thing can be done" is a common situation in these expressions (e.g. I can't do but others can do, I won't tell him but will tell others, You can't buy it at this price, but can buy it at a higher price).