orientdb property constraints like MANDATORY not failing on improper java api insertions

I have an orientdb setup with a class called MessageLog with a property messageId that has a constraint MANADATORY and NOT NULL. If i try to insert a record from the console with a null messageId it raises an exception telling that the property cannot be null. But when i do a simple insertion from the Java API the record is inserted with the property value null. How is that possible.

The java code is:

import com.tinkerpop.blueprints.Vertex;
import com.tinkerpop.blueprints.impls.orient.OrientGraph;
import com.tinkerpop.blueprints.impls.orient.OrientVertexType;

public class OrientDbTrials {

public static void main(String[] args) {

    OrientGraph graph = new OrientGraph("remote:localhost/blah","root","*****");
    System.out.println("Connected to the db.");

    Vertex messageLog = graph.addVertex("class:MessageLog");

    System.out.println("Created new vertex : " + messageLog.toString());
    messageLog.setProperty("messageId", null);
    graph.commit();
    System.out.println("Successfully saved it.");

    }

}

Can somebody please explain this.