src/main/java/io/reactivex/Completable.java
private static NullPointerException toNpe(Throwable ex) {
        NullPointerException npe = new NullPointerException("Actually not, but can't pass out an exception otherwise...");
        npe.initCause(ex);
        return npe;
    }
private static NullPointerException toNpe(Throwable ex) {
        NullPointerException npe = new NullPointerException("Actually not, but can't pass out an exception otherwise...");
        npe.initCause(ex);
        return npe;
    }
Creates a NullPointerException instance and sets the given Throwable as its initial cause.
@param ex the Throwable instance to use as cause, not null (not verified)
@return the created NullPointerException