Looks good to me. I've left some comments that should be addressed I think.

Do you by any chance know why this is happening for the javac compiler only? Is it a bug that we should perhaps report?

fixed the commented bits. The reason it happens for the javac compiler is because it does what the API says. We called a method with a primitive type that should not be called with a primitive type. The eclipse compiler is less restrictive apparently.

excerpt from the API:

{@return the type corresponding to a type element and actual type arguments} Given the type element for Set and the type mirror for String, for example, this method may be used to get the parameterized type Set<String>.

....

IllegalArgumentException - if too many or too few type arguments are given, or if an inappropriate type argument or type element is provided

Logically a primitive cannot be a type argument, you will need to use the boxed version of it. (Integer instead of int)
So in this case we were calling it with an inappropriate type argument.