Check if staking address exists first

contracts/vesting/src/contract.rs

@@ -313,6 +313,11 @@ fn try_update_staking_address(
     info: MessageInfo,
     deps: DepsMut<'_>,
 ) -> Result<Response, ContractError> {
+    if let Some(ref to_address) = to_address {
+        if let Ok(_account) = account_from_address(&to_address, deps.storage, deps.api) {
+            return Err(ContractError::StakingAccountExists(to_address.to_string()));
+        }
+    }
     let address = info.sender.clone();
     let to_address = to_address.and_then(|x| deps.api.addr_validate(&x).ok());
     let mut account = account_from_address(info.sender.as_str(), deps.storage, deps.api)?;

contracts/vesting/src/errors.rs

@@ -52,4 +52,6 @@ pub enum ContractError {
     LockedPledgeCapReached { current: Uint128, cap: Uint128 },
     #[error("VESTING: ({}: Account owned by {owner} has unpopulated vesting periods!", line!())]
     UnpopulatedVestingPeriods { owner: Addr },
+    #[error("VESTING: Vesting account associated with {0} already exists, only addresses with not existing vesting accounts can be added as staking addresses")]
+    StakingAccountExists(String),
 }