src/main/java/io/reactivex/internal/observers/BlockingMultiObserver.java
public Throwable blockingGetError() {
        if (getCount() != 0) {
            try {
                BlockingHelper.verifyNonBlocking();
                await();
            } catch (InterruptedException ex) {
                dispose();
                return ex;
            }
        }
        return error;
    }
public Throwable blockingGetError() {
        if (getCount() != 0) {
            try {
                BlockingHelper.verifyNonBlocking();
                await();
            } catch (InterruptedException ex) {
                dispose();
                return ex;
            }
        }
        return error;
    }
Block until the latch is counted down and return the error received or null if no
error happened.
@return the error received or null