Add checks for zero values in addresses in protect_position

src/vault.cairo

@@ -235,7 +235,9 @@ mod Vault {
             let caller = get_caller_address();
             let vault_owner = self.ownable.owner();
             let current_amount = self.amounts.entry(caller).read();
-
+
+            assert(deposit_contract.is_non_zero(), 'Deposit contract is zero');
+            assert(user.is_non_zero(), 'User address is zero');
             assert(vault_owner == caller || user == caller, 'Caller must be owner or user');
             assert(current_amount >= amount, 'Insufficient balance');