src/main/java/io/reactivex/plugins/RxJavaPlugins.java
@NonNull
    static Scheduler applyRequireNonNull(@NonNull Function<? super Callable<Scheduler>, ? extends Scheduler> f, Callable<Scheduler> s) {
        return ObjectHelper.requireNonNull(apply(f, s), "Scheduler Callable result can't be null");
    }
@NonNull
    static Scheduler applyRequireNonNull(@NonNull Function<? super Callable<Scheduler>, ? extends Scheduler> f, Callable<Scheduler> s) {
        return ObjectHelper.requireNonNull(apply(f, s), "Scheduler Callable result can't be null");
    }
Wraps the call to the Scheduler creation function in try-catch and propagates thrown
checked exceptions as RuntimeException and enforces that result is not null.
@param f the function to call, not null (not verified). Cannot return null
@param s the parameter value to the function
@return the result of the function call, not null
@throws NullPointerException if the function parameter returns null