Prior to this commit, `MockHttpServletResponse#setHeader` would not remove the header entry when given a `null` value, as documented in the Servlet API. This commit ensures that this behavior is enforced. Fixes gh-34464
Prior to this commit, `MockHttpServletResponse#setHeader` would not remove the header entry when given a `null` value, as documented in the Servlet API. This commit ensures that this behavior is enforced. Fixes gh-34464