@Override
  public MutableTreeRootHolder setRoots(Component root, Component reportRoot) {
    checkState(this.root == null, "root can not be set twice in holder");
    this.root = requireNonNull(root, "root can not be null");
    this.extendedTreeRoot = requireNonNull(reportRoot, "extended tree root can not be null");
    return this;
  }
@Test
  public void setRoots_throws_NPE_if_root_is_null() {
    assertThatThrownBy(() -> underTest.setRoots(null, DUMB_PROJECT))
      .isInstanceOf(NullPointerException.class)
      .hasMessage("root can not be null");
  }