src/main/java/io/reactivex/parallel/ParallelFlowable.java
@CheckReturnValue
    @NonNull
    public final ParallelFlowable<T> doOnNext(@NonNull Consumer<? super T> onNext, @NonNull ParallelFailureHandling errorHandler) {
        ObjectHelper.requireNonNull(onNext, "onNext is null");
        ObjectHelper.requireNonNull(errorHandler, "errorHandler is null");
        return RxJavaPlugins.onAssembly(new ParallelDoOnNextTry<T>(this, onNext, errorHandler));
    }
@CheckReturnValue
    @NonNull
    public final ParallelFlowable<T> doOnNext(@NonNull Consumer<? super T> onNext, @NonNull ParallelFailureHandling errorHandler) {
        ObjectHelper.requireNonNull(onNext, "onNext is null");
        ObjectHelper.requireNonNull(errorHandler, "errorHandler is null");
        return RxJavaPlugins.onAssembly(new ParallelDoOnNextTry<T>(this, onNext, errorHandler));
    }
Call the specified consumer with the current element passing through any 'rail' and
handles errors based on the given {@link ParallelFailureHandling} enumeration value.
<p>History: 2.0.8 - experimental
@param onNext the callback
@param errorHandler the enumeration that defines how to handle errors thrown
from the onNext consumer
@return the new ParallelFlowable instance
@since 2.2