 	private var mNextDataTable:		CNMappingTable?
 	private var mNextFieldNames:		Array<FieldName>?
 	private var mNextRecordMappingFunction:	FilterFunction?
-	private var mNextVirtualFields:		Dictionary<String, CNMappingTable.VirtualFieldCallback>
+	private var mNextVirtualFields:		Dictionary<String, CNMappingTable.VirtualFieldCallback>?
 
 	private var mHasHeader:			Bool
 	private var mIsEnable:			Bool

		mFieldNames		= fields
		mNextDataTable		= nil
		mNextFieldNames		= nil
		mNextVirtualFields	= [:]
		mMinimumVisibleRowCount	= 8
		mHasHeader		= false
		mIsEnable		= false

		case .ok(_):
			break
		case .error(let err):
			CNLog(logLevel: .error, message: err.toString(), atFunction: #function, inFile: #file)
		@unknown default:
			CNLog(logLevel: .error, message: "Unknown error", atFunction: #function, inFile: #file)
		}
		let path      = CNValuePath(identifier: nil, elements: [.member("table")])
		let table     = CNValueTable(path: path, valueStorage: storage)
