Cant create server pages in node pages

based on main branch

Log:

Page must be placed in graph or other page. java.lang.IllegalArgumentException: Page must be placed in graph or other page. at org.eclipse.glsp.example.javaemf.handler.NodeCreation.CreatePageHandler.getParentElement(CreatePageHandler.java:73) at org.eclipse.glsp.example.javaemf.handler.DiNeROS.ElementCreation.CreateServerPageHandler.createCommand(CreateServerPageHandler.java:31) at org.eclipse.glsp.example.javaemf.handler.DiNeROS.ElementCreation.CreateServerPageHandler.createCommand(CreateServerPageHandler.java:16) at org.eclipse.glsp.server.operations.OperationHandler.execute(OperationHandler.java:66) at org.eclipse.glsp.server.operations.OperationActionHandler.executeHandler(OperationActionHandler.java:63) at org.eclipse.glsp.server.operations.OperationActionHandler.lambda$executeOperation$0(OperationActionHandler.java:58) at java.base/java.util.Optional.map(Optional.java:260) at org.eclipse.glsp.server.operations.OperationActionHandler.executeOperation(OperationActionHandler.java:58) at org.eclipse.glsp.server.operations.OperationActionHandler.executeAction(OperationActionHandler.java:53) at org.eclipse.glsp.example.javaemf.handler.ExtendedOperationActionHandler.executeAction(ExtendedOperationActionHandler.java:19) at org.eclipse.glsp.example.javaemf.handler.ExtendedOperationActionHandler.executeAction(ExtendedOperationActionHandler.java:11) at org.eclipse.glsp.server.actions.AbstractActionHandler.execute(AbstractActionHandler.java:53) at org.eclipse.glsp.server.internal.actions.DefaultActionDispatcher.runAction(DefaultActionDispatcher.java:198) at org.eclipse.glsp.server.internal.actions.DefaultActionDispatcher.handleAction(DefaultActionDispatcher.java:176) at org.eclipse.glsp.example.javaemf.handler.MyActionDispatcher.handleAction(MyActionDispatcher.java:24) at org.eclipse.glsp.server.internal.actions.DefaultActionDispatcher.handleNextAction(DefaultActionDispatcher.java:163) at org.eclipse.glsp.server.internal.actions.DefaultActionDispatcher.runThread(DefaultActionDispatcher.java:149) at java.base/java.lang.Thread.run(Thread.java:840)