@Override
  public void setUserData(final ZyNodeData<?> data) {
    Preconditions.checkNotNull(data, "Error: Invalid node data");
    Preconditions.checkArgument(
        (data.getNode().getRawNode() instanceof IGroupNode),
        "Error: User data does not contain a group node");

    m_userData = data;
  }
Returns the user data associated with the realizer.

@return The user data associated with the realizer.
java/zylib/src/main/java/com/google/security/zynamics/zylib/yfileswrap/gui/zygraph/realizers/ZyGroupNodeRealizer.java