 you do not set these properties, all port identifiers are assumed to be the empty string,
  which is the name of the one default port for a node.
</p>
<p class="box bg-danger">
  If you have set or bound <a>GraphObject.portId</a> on any element to be a non-empty string,
  you will need to use a <a>GraphLinksModel</a> and set <a>GraphLinksModel.linkToPortIdProperty</a>
  and <a>GraphLinksModel.linkFromPortIdProperty</a> to be the names of two properties on your link data,
  or you will need to hard code the