@Override
    public void read(JmeImporter im) throws IOException {
        super.read(im);
        InputCapsule c = im.getCapsule(this);
        name = c.readString("name", null);
        size = c.readInt("size", 0);
        patchSize = c.readInt("patchSize", 0);
        stepScale = (Vector3f) c.readSavable("stepScale", null);
        offset = (Vector2f) c.readSavable("offset", null);
        offsetAmount = c.readFloat("offsetAmount", 0);
        gridTileLoader = (TerrainGridTileLoader) c.readSavable("terrainQuadGrid", null);
        material = (Material) c.readSavable("material", null);
        initData();
        if (gridTileLoader != null) {
            gridTileLoader.setPatchSize(this.patchSize);
            gridTileLoader.setQuadSize(this.quadSize);
        }
    }
This will print out any exceptions from the thread
jme3-terrain/src/main/java/com/jme3/terrain/geomipmap/TerrainGrid.java