src/main/java/io/reactivex/subjects/BehaviorSubject.java
public boolean hasValue() {
        Object o = value.get();
        return o != null && !NotificationLite.isComplete(o) && !NotificationLite.isError(o);
    }
public boolean hasValue() {
        Object o = value.get();
        return o != null && !NotificationLite.isComplete(o) && !NotificationLite.isError(o);
    }
Returns true if the subject has any value.
<p>The method is thread-safe.
@return true if the subject has any value