The @NullMarked annotation on DataFetchingEnvironment makes type parameters implicitly non-null, but java-dataloader's DataLoader declares V extends @nullable Object to allow nullable values.

This mismatch prevents Kotlin consumers from expressing nullable value types without unsafe casts when returning CompletableFuture from data fetchers.

Add explicit V extends @nullable Object bound to match DataLoader's type signature, enabling proper nullability propagation to Kotlin.

#4179