Added logic to pull tkn_remove from nft in remove_liquidity if necessary

hydradx/model/amm/omnipool_amm.py

@@ -1149,6 +1149,10 @@ def remove_liquidity(self, agent: Agent, quantity: float = None, tkn_remove: str
         #     k = (self.unique_id + "_" + str(i), tkn_remove)
 
         k = (self.unique_id, tkn_remove)
+        if nft_id is not None:
+            if nft_id not in agent.nfts:
+                return self.fail_transaction('Agent does not have liquidity position with specified nft_id.', agent)
+            tkn_remove = agent.nfts[nft_id].tkn
 
         if tkn_remove not in self.asset_list:
             for sub_pool in self.sub_pools.values():
@@ -1161,7 +1165,7 @@ def remove_liquidity(self, agent: Agent, quantity: float = None, tkn_remove: str
                     else:
                         return self
 
-            raise AssertionError(f"invalid value for i: {tkn_remove}")
+            raise AssertionError(f"invalid value for tkn_remove: {tkn_remove}")
 
         if quantity == 0:
             return self