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_CREATE_NEW_PARAMETER;
					}
					else
					{
						value = getDummyText( paramHandle ) + paramName;
					}
				}
				else if ( columnIndex == 1 )
				{
					if ( !isSingle( ) || paramHandle == getFirstParameter( ) )
					{
						value = LABEL_SELECT_DATA_SET;
					}
				}
				else if ( columnIndex == 2 )
				{
					if ( isSingle( ) && paramHandle != getFirstParameter( ) )
					{
						value = LABEL_SELECT_VALUE_COLUMN;
					}
				}
			}
			else
			{
				switch ( columnIndex )
				{
					case 0 :
					{
						if ( paramHandle != newParameter )