Bug 152430 Key can modify to empty string
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/command/PropertyCommand.java
public void setMember( MemberRef ref, Object value )
			throws SemanticException
	{
		PropertyDefn memberDefn = ref.getMemberDefn( );
		PropertyDefn propDefn = ref.getPropDefn( );
		assert propDefn != null;
		assertExtendedElement( module, element, propDefn );
		assert memberDefn != null;
		value = memberDefn.validateValue( module, value );
		
		
		if ( memberDefn.getTypeCode( ) == PropertyType.NAME_TYPE
				|| memberDefn.getTypeCode( ) == PropertyType.MEMBER_KEY_TYPE )
			checkItemName( ref, (String) value );
		
		
		
		Object oldValue = ref.getLocalValue( module, element );
		if ( oldValue == null && value == null )
			return;
		if ( oldValue != null && value != null && oldValue.equals( value ) )
			return;
		
		ActivityStack stack = getActivityStack( );
		String label = ModelMessages
				.getMessage( MessageConstants.CHANGE_ITEM_MESSAGE );
		stack.startTrans( label );
		makeLocalCompositeValue( ref );
		MemberRecord record = new MemberRecord( module, element, ref, value );
		stack.execute( record );