[Workbench] Crashes with Fiddlesticks when trying to view a pipeline instance graph copied from another cluster
See #7001 for original bug report and details. This happens because Workbench tries to look up jobs from other clusters, fails and gets nil as a response, but assumes it has a real object.
When we're rendering this graph, any time we try to look up an object, we should check for nil and draw a stub when we get it. Just render the object in the graph by the provided UUID, without trying to introspect any further.