Silent failure in add_account_to_whitelist method

The add_account_to_whitelist method in the provided code has a silent failure vulnerability. The method attempts to add an account to the whitelist using the insert function, but it does not handle the case when the account already exists in the whitelist.

When the insert function is called with a key that already exists in the map, it returns false. However, the add_account_to_whitelist method does not check the return value of insert and does not provide any feedback or error handling mechanism to indicate that the account was not added to the whitelist due to its presence.

The caller of the method is not informed whether the account was successfully added to the whitelist or if it already existed.

If the account already exists in the whitelist, panic with a meaningful error message indicating that the account is already whitelisted.

Example:

pub fn add_account_to_whitelist(&mut self, token: AccountId, account: AccountId) {
    assert!(
        self.whitelist_tokens.get(&token).is_some(),
        "The whitelisted token mode is not set"
    );
    let token_account_key = get_token_account_key(token, account);
    assert!(
        self.whitelist_accounts.insert(&token_account_key),
        "Account is already whitelisted for the given token"
    );
}

Acknowledged.