Opening a BPMN diagram gives the "Could not open the editor..." error

Double-click the .bpmx model from the Project Explorer in order to open the BPMN diagram. The Could not open the editor: An unexpected exception was thrown error will appear as in the screenshot:

The following output is generated in the .log file:

!MESSAGE Unable to create editor ID com.ibm.xtools.bpmn2.ui.diagram.internal.part.Bpmn2DiagramEditorID: An unexpected exception was thrown.

!STACK 0

java.lang.NullPointerException

at org.eclipse.gmf.runtime.diagram.ui.services.editpart.EditPartService.createEditPart(Unknown Source)

at org.eclipse.gef.ui.parts.AbstractEditPartViewer.setContents(Unknown Source)

at org.eclipse.gmf.runtime.diagram.ui.parts.DiagramEditor.initializeGraphicalViewerContents(Unknown Source)

at com.ibm.xtools.bpmn2.modeler.ui.internal.editor.CustomBpmn2DiagramEditorWithHeader.initializeGraphicalViewerContents(Unknown Source)

at org.eclipse.gmf.runtime.diagram.ui.parts.DiagramEditor.initializeGraphicalViewer(Unknown Source)...

It is not possible to open the BPMN diagram.

You modified a model that had dependencies on another model, which means that your changes to the first model caused the second one to change as well.

However, although you saved the changes to the first model and then closed it, you did not save the changes to the second model, before you closed it.

As a result, the two models are no longer synchronized with each other and there are broken references that cause the second BPMN model to be corrupted.

WORKAROUND

Load the BPMN model that throws the error into a new workspace in order to recover the diagram.