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
{
							String paramName;
							if ( paramHandle != selectedParameter )
							{
								paramName = paramHandle.getName( );
							}
							else
							{
								paramName = paramNameEditor.getText( ).trim( );
							}
							value = getDummyText( paramHandle ) + paramName;
						}
						break;
					}
					case 1 :
					{
						DataSetHandle dataSet = null;
						if ( isSingle( ) )
						{
							if ( paramHandle != getFirstParameter( ) )
							{
								break;
							}
							dataSet = inputParameterGroup.getDataSet( );
						}
						else
						{
							dataSet = getDataSet( paramHandle );
						}
						if ( dataSet == null )