Transaction

[Error Code: 1101] error caused by: 1 error occurred:
	* transaction execute failed: [Error Code: 1101] cadence runtime error: Execution failed:
  --> 6005636753f0a7b0cb974208064861a999f2e42ac28b07fcc560c6b8240abb3b:48:19
   |
48 |         let nft <- pool.unstake(userCertificate: userCertificate, tokenId: nftId)
   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: unexpectedly found nil while forcing an Optional value
   --> 1b77ba4b414de352.StakingNFT:668:25
    |
668 |       let userInfoRef = (&self.usersInfo[userAddress] as &UserInfo?)!
    |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^