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/ParameterDialog.java
}
	}
	private void clearDefaultValueChooser( boolean isChecked )
	{
		if ( isChecked )
		{
			clearDefaultValueText( );
			clearDefaultValueChooserSelections( );
		}
		else
		{
			if ( defaultValueChooser == null
					|| defaultValueChooser.getItemCount( ) > 1 )
				return;
			defaultValueChooser.add( CHOICE_NULL_VALUE );
			defaultValueChooser.add( CHOICE_BLANK_VALUE );
		}
	}
	private void clearArea( Composite area )
	{
		Control[] children = area.getChildren( );
		for ( int i = 0; i < children.length; i++ )
		{
			children[i].dispose( );
		}
	}
	private void updateTableButtons( )
	{
		boolean isEnable = true;
		SelectionChoice selectedChoice = null;