Setting NBT

[WiebeHero]

So i am WiebeHero and i want to set NBT on my weapon/tools this is about atribute modifiers.
the error i got is: the NBT of clicked item is neither an item stack nor an entity type!
Hope you can help me with this.
error line: set "{AttributeModifiers:[{AttributeName:""generic.attackDamage"",Name:""generic.attackDamage"",Amount:0.0,Operation:0,UUIDLeast:324464,UUIDMost:154531,Slot:""mainhand""},{AttributeName:""generic.attackSpeed"",Name:""generic.attackSpeed"",Amount:0,Operation:0,UUIDLeast:8055,UUIDMost:772149,Slot:""mainhand""}]}" of nbt of clicked item
Here is the full code:

on inventory click:
    if cursor slot of player is stone hoe:
        if lore of cursor slot of player contains "&7Upgrade Progress: 0 / 2":
            if lore of clicked item contains "&7Upgrade Progress: 1 / 2":
                cancel event
                set "{AttributeModifiers:[{AttributeName:""generic.attackDamage"",Name:""generic.attackDamage"",Amount:0.0,Operation:0,UUIDLeast:324464,UUIDMost:154531,Slot:""mainhand""},{AttributeName:""generic.attackSpeed"",Name:""generic.attackSpeed"",Amount:0,Operation:0,UUIDLeast:8055,UUIDMost:772149,Slot:""mainhand""}]}" of nbt of clicked item
                set cursor of player to air

 

[White]

Replace "of" to "to" before nbt. Also replace set to add if it still throws an error.