DGM.retainAll() has wrong generic type on Closure condition

DGM's retainAll() has this signature:

public static <T> boolean retainAll(Collection<T> self, @ClosureParams(FirstParam.FirstGenericType.class) Closure<T> condition)

The condition closure is expected to return a boolean or a boolean-ish value, but not the same type as the Collection.

removeAll() has the correct signature that doesn't specify a return type on the closure:

public static <T> boolean removeAll(Collection<T> self, @ClosureParams(FirstParam.FirstGenericType.class) Closure condition)

retainAll() still works, but IDEA's syntax highlighting complains when passing in a Closure<Boolean> to retainAll() on a List of other objects.