As raised and discuss on KT-19592 Kotlin issue, null-safety of Spring API does not apply to generic type arguments. To do so, after KT-19592 being fixed we would have to use ElementType.TYPE_USE but its scope is too wide to make it usable for us at @TypeQualifierDefault level of @Nullable and @NonNullApi.
Another solution would be to add ElementType.TYPE_USE at @Target and annotate every generic type argument of Spring API, maybe that could be done via introducing a @NonNull annotation that would also be useful for #20311.
Juergen Hoeller I have added my feedback on their PR. My main concern is that current plan is to have a Kotlin centric meta-annotations library instead of a JVM one that could be use for more wide use cases, including pure Java projects.