output: #fixed code
                                  @Override
      public Result<Balance> getBalance(byte[] address) throws NulsException {
          if (address == null || address.length != AddressTool.HASH_LENGTH) {
              return Result.getFailed(AccountLedgerErrorCode.PARAMETER_ERROR);
          }
  
          if (!isLocalAccount(address)) {
              return Result.getFailed(AccountLedgerErrorCode.ACCOUNT_NOT_EXIST);
          }
  
          Balance balance = balanceManager.getBalance(address).getData();
  
          if (balance == null) {
              return Result.getFailed(AccountLedgerErrorCode.ACCOUNT_NOT_EXIST);
          }
  
          return Result.getSuccess().setData(balance);
      }
input: #vulnerable code 
                                  @Override
      public Result<Balance> getBalance(byte[] address) throws NulsException {
          if (address == null || address.length != AddressTool.HASH_LENGTH) {
              return Result.getFailed(AccountLedgerErrorCode.PARAMETER_ERROR);
          }
  
          if (!isLocalAccount(address)) {
              return Result.getFailed(AccountLedgerErrorCode.ACCOUNT_NOT_EXIST);
          }
  
          Balance balance = balanceProvider.getBalance(address).getData();
  
          if (balance == null) {
              return Result.getFailed(AccountLedgerErrorCode.ACCOUNT_NOT_EXIST);
          }
  
          return Result.getSuccess().setData(balance);
      } 
                              #location 11 
                              #vulnerability type THREAD_SAFETY_VIOLATION