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
{
							value = LABEL_SELECT_DATA_SET;
						}
						else
						{
							value = dataSet.getName( );
						}
						break;
					}
					case 2 :
					{
						if ( paramHandle.getValueExpr( ) != null )
						{
							value = getColumnName( paramHandle, COLUMN_VALUE );
						}
						else if ( getDataSetColumns( paramHandle, true ).length > 0 )
						{
							value = LABEL_SELECT_VALUE_COLUMN;
						}
						else
						{
							value = LABEL_NO_COLUMN_AVAILABLE;
						}
						break;
					}
					case 3 :
					{
						value = getColumnName( paramHandle, COLUMN_DISPLAY_TEXT );
						if ( value == null )
						{