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
}
				else if ( COLUMN_DISPLAY_TEXT.equals( property ) )
				{
					value = getColumnName( parameter, COLUMN_DISPLAY_TEXT );
				}
				if ( value == null )
				{
					value = ""; 
				}
				return value;
			}
			return ""; 
		}
		public void modify( Object element, String property, Object value )
		{
			Object actualElement = ( (TableItem) element ).getData( );
			try
			{
				saveParameterProperties( );
			}
			catch ( SemanticException e1 )
			{
				e1.printStackTrace( );
			}
			if ( COLUMN_NAME.equals( property ) )
			{
				try
				{
					( (ScalarParameterHandle) actualElement ).setName( (String) value );
					givenName = true;