driver-core/src/main/com/mongodb/operation/AggregateOperation.java
public BsonDocument getHint() {
        BsonValue hint = wrapped.getHint();
        if (hint == null) {
            return null;
        }
        if (!hint.isDocument()) {
            throw new IllegalArgumentException("Hint is not a BsonDocument please use the #getHintBsonValue() method. ");
        }
        return hint.asDocument();
    }
public BsonDocument getHint() {
        BsonValue hint = wrapped.getHint();
        if (hint == null) {
            return null;
        }
        if (!hint.isDocument()) {
            throw new IllegalArgumentException("Hint is not a BsonDocument please use the #getHintBsonValue() method. ");
        }
        return hint.asDocument();
    }
Returns the hint for which index to use. The default is not to set a hint.

@return the hint
@since 3.6
@mongodb.server.release 3.6