Hello material error

I work to code this tutorial https://wiki.jmonkeyengine.org/legacy/doku.php/jme3:beginner:hello_material and doing exercise 1 but, it show error not found, I try to change my path to

cube_leak.setMaterial((Material)assetManager.loadMaterial(“Common/Materials/LeakThrough.j3m”));

but it’s still not working

How?