uniqueLabel property
If defined, this is the label used to check if the item has other items of matching types already equipped. For instance, when you aren't allowed to equip more than one Exotic Weapon, that's because all exotic weapons have identical uniqueLabels and the game checks the to-be-equipped item's uniqueLabel vs. all other already equipped items (other than the item in the slot that's about to be occupied).
Implementation
@JsonKey(name:'uniqueLabel')
String? uniqueLabel;