eclipse not inserting "diamond" operator in a java 8 project

I had this issue just a few minutes ago and solved it half way through typing out an SO question.

Eclipse's auto-complete apparently prioritized the old-style generic syntax after I had fiddled with the advanced content assist settings a while ago. Try resetting Java > Editor > Content Assist > Advanced to defaults; this was what fixed it for me and returned auto-complete to inserting the diamond syntax by default.

I had the same problem but the solution to set everything to default didn't work for me. What worked for me is Java > Editor > Content Assist > Advanced and unchecking JPA Proposals in the upper window.