EDIT

         <dynamic

               class="eu.etaxonomy.taxeditor.view.CdmViewerContextMenu"

               id="eu.etaxonomy.taxeditor.navigation.cdmViewerContextMenu">

         </dynamic>

 eu.etaxonomy.taxeditor.handler.defaultHandler,

      <command

            defaultHandler="eu.etaxonomy.taxeditor.handler.defaultHandler.DefaultOpenClassificationWizardHandler"

            id="eu.etaxonomy.taxeditor.command.openClassificationWizard"

            name="Open Classification Wizard">

         <commandParameter

               id="eu.etaxonomy.taxeditor.command.openClassificationWizard.uuid"

               name="Classification Uuid"

               optional="true"

               typeId="eu.etaxonomy.taxeditor.uuidParameterType">

         </commandParameter>

      </command>

   </extension>

   <extension

         point="org.eclipse.ui.commands">

      <commandParameterType

            converter="eu.etaxonomy.taxeditor.handler.UuidsParameterTypeConverter"

            id="eu.etaxonomy.taxeditor.uuidParameterType"

            type="java.util.UUID">

      </commandParameterType>

<extension

      point="eu.etaxonomy.taxeditor.store.cdmViewer">

   <viewCommandMapping

         commandId="eu.etaxonomy.taxeditor.command.openClassificationWizard"

         selection="eu.etaxonomy.cdm.model.taxon.Classification"

         viewerName="Classification Wizard">

   </viewCommandMapping>

</extension>

package eu.etaxonomy.taxeditor.handler;

import java.util.UUID;

import org.eclipse.core.commands.AbstractParameterValueConverter;

import org.eclipse.core.commands.ParameterValueConversionException;

/**

 * Converts {@link UUID}s to a string representation

 * and vica versa.

 *

 * @author pplitzner

 * @date Sep 15, 2015

 *

 */

public class UuidsParameterTypeConverter extends AbstractParameterValueConverter {

    public UuidsParameterTypeConverter() {

    }

    @Override

    public Object convertToObject(String parameterValue) throws ParameterValueConversionException {

        return UUID.fromString(parameterValue);

    }

    @Override

    public String convertToString(Object parameterValue) throws ParameterValueConversionException {

        return parameterValue.toString();

    }

}

package eu.etaxonomy.taxeditor.handler.defaultHandler;

import java.util.UUID;

import org.eclipse.core.commands.AbstractHandler;

import org.eclipse.core.commands.ExecutionEvent;

import org.eclipse.core.commands.ExecutionException;

import org.eclipse.core.commands.ParameterType;

import org.eclipse.core.commands.common.NotDefinedException;

import org.eclipse.jface.viewers.ISelection;

import org.eclipse.jface.viewers.IStructuredSelection;

import org.eclipse.jface.wizard.WizardDialog;

import org.eclipse.ui.PlatformUI;

import org.eclipse.ui.handlers.HandlerUtil;

import eu.etaxonomy.cdm.api.service.IClassificationService;

import eu.etaxonomy.cdm.model.taxon.Classification;

import eu.etaxonomy.taxeditor.model.MessagingUtils;

import eu.etaxonomy.taxeditor.newWizard.NewClassificationWizard;

import eu.etaxonomy.taxeditor.store.CdmStore;

public class DefaultOpenClassificationWizardHandler extends AbstractHandler {

    @Override

    public Object execute(ExecutionEvent event) throws ExecutionException {

        String commandId = event.getCommand().getId();

        String uuidParameterId = commandId+".uuid";

        //check if uuid parameter is set

        if(event.getParameter(uuidParameterId)!=null){

            Object object = event.getObjectParameterForExecution(uuidParameterId);

            ParameterType parameterType;

            try {

                parameterType = event.getCommand().getParameterType(uuidParameterId);

                if(parameterType.isCompatible(object)){

                    Classification classification = CdmStore.getService(IClassificationService.class).load((UUID) object);

                    openClassificationWizard(event, classification);

                }

            } catch (NotDefinedException e) {

                MessagingUtils.error(DefaultOpenClassificationWizardHandler.class, "Error while opening classification!", e);

            }

        }

        //if not try current selection

        else{

            ISelection selection = HandlerUtil.getCurrentSelection(event);

            if(selection instanceof IStructuredSelection){

                final IStructuredSelection structuredSelection = (IStructuredSelection) selection;

                if(structuredSelection.size() == 1 && structuredSelection.getFirstElement() instanceof Classification){

                    Classification classification = (Classification) structuredSelection.getFirstElement();

                    openClassificationWizard(event, classification);

                }

            }

        }

        return null;

    }

    private void openClassificationWizard(ExecutionEvent event, Classification classification) {

        NewClassificationWizard classificationWizard = new NewClassificationWizard();

        classificationWizard.init(null, null);

        classificationWizard.setEntity(classification);

        WizardDialog dialog = new WizardDialog(PlatformUI.getWorkbench().getActiveWorkbenchWindow().getShell(), classificationWizard);

        dialog.open();

    }

}