Integer property in ListElement should be undefined if there is no value assigned explicitly

ListModel {
    ListElement { type: "Command"; commandId: 1 } 
    ListElement { type: "Command"; commandId: 2 } 
    ListElement { type: "NotCommand"; } 
}

The ListElement with type "Command" will assign commandId with integer.
The type "NotCommand" will not assign commandId at all.
The bug is that when access the commandId of the third item, it will return an integer value 0.
Actually, i expect the value as undefined. if the commandId is string value, the value is undefined as expected.