Bug 182673 No default value error message prompts incorrectly
Steps to reproduce: 1. New a report parameter; 2. Choose control type as Combo; 3. Choose parameter as dynamic type; Expected result: As the isRequired is false by default, parameter's default value can be null value. There should be no error message about no default value prompt. Actual result; Error messages prompts
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/CascadingParametersDialog.java
import org.eclipse.birt.report.designer.internal.ui.util.DataUtil;
import org.eclipse.birt.report.designer.internal.ui.util.ExceptionHandler;
import org.eclipse.birt.report.designer.internal.ui.util.IHelpContextIds;
import org.eclipse.birt.report.designer.internal.ui.util.UIUtil;
import org.eclipse.birt.report.designer.nls.Messages;
import org.eclipse.birt.report.designer.ui.newelement.DesignElementFactory;
import org.eclipse.birt.report.designer.ui.views.attributes.providers.ChoiceSetFactory;
import org.eclipse.birt.report.designer.ui.widget.ComboBoxCellEditor;
import org.eclipse.birt.report.designer.util.DEUtil;
import org.eclipse.birt.report.model.api.CachedMetaDataHandle;
import org.eclipse.birt.report.model.api.CascadingParameterGroupHandle;
import org.eclipse.birt.report.model.api.DataSetHandle;
import org.eclipse.birt.report.model.api.ResultSetColumnHandle;
import org.eclipse.birt.report.model.api.ScalarParameterHandle;
import org.eclipse.birt.report.model.api.activity.SemanticException;
import org.eclipse.birt.report.model.api.command.NameException;
import org.eclipse.birt.report.model.api.elements.DesignChoiceConstants;
import org.eclipse.birt.report.model.api.elements.ReportDesignConstants;
import org.eclipse.birt.report.model.api.metadata.IChoice;
import org.eclipse.birt.report.model.api.metadata.IChoiceSet;
import org.eclipse.birt.report.model.api.util.StringUtil;
import org.eclipse.jface.util.Assert;
import org.eclipse.jface.viewers.CellEditor;
import org.eclipse.jface.viewers.ICellModifier;
import org.eclipse.jface.viewers.ILabelProviderListener;
import org.eclipse.jface.viewers.ISelection;
import org.eclipse.jface.viewers.ISelectionChangedListener;
import org.eclipse.jface.viewers.IStructuredContentProvider;
import org.eclipse.jface.viewers.IStructuredSelection;
import org.eclipse.jface.viewers.ITableLabelProvider;