Fails to set mass and inertia when using b2FixtureDef

[eweitnauer]

There seems to be a problem when using b2FixtureDef to create a fixture. With the following code

function createBody(x, y, rot, dynamic) {
    var bodyDef = new Box2D.b2BodyDef();
    bodyDef.set_position(new Box2D.b2Vec2(x, y));
    bodyDef.set_angle(rot);
    bodyDef.set_type(dynamic ? Box2D.b2_dynamicBody : Box2D.b2_staticBody);
    var body = world.CreateBody(bodyDef);
    var shape = new Box2D.b2PolygonShape();
    shape.SetAsBox(1, 0.1);
    var fixtureDef = new Box2D.b2FixtureDef();
    fixtureDef.set_density(1);
    fixtureDef.set_shape(shape);
    body.CreateFixture(fixtureDef);
    return body;
  }

I get the error "Uncaught Assertion failed: m_I > 0.0f, at Box2D_v2.2.1/Box2D/Dynamics/b2Body.cpp, 319, void b2Body::ResetMassData()".
What I was also wondering about is why the b2MassData is not available as javascript class in the Box2D namespace.