NOAH

Addresses should be checked before assignment or external call to make sure they are not zero addresses. ```solidity=18 admin = _admin; ``` - `_admin` is not zero-checked before being used. --- ```solidity=47 feeTo = _feeTo; ``` - `_feeTo` is not zero-checked before being used. --- ```solidity=52 admin = _admin; ``` - `_admin` is not zero-checked before being used. --- ```solidity=73 token0 = _token0; ``` - `_token0` is not zero-checked before being used. --- ```solidity=74 token1 = _token1; ``` - `_token1` is not zero-checked before being used. --- ```solidity=25 factory = _factory; ``` - `_factory` is not zero-checked before being used. --- ```solidity=26 WETH = _WETH; ``` - `_WETH` is not zero-checked before being used.

The return value of the transfer()/transferFrom() call is not checked. ```solidity=137 INoahPair(pair).transferFrom(msg.sender, pair, liquidity); // send liquidity to pair ```

The return value of an external call is not stored in a local or state variable. ```solidity=44 INoahFactory(factory).createPair(tokenA, tokenB); ```

```solidity=19 address public factory; ``` The above variables assigned in the constructor can be declared as `immutable`. Immutable state variables can be assigned during contract creation but will remain constant throughout the lifetime of a deployed contract. A big advantage of immutable variables is that reading them is significantly cheaper than reading from regular state variables since they will not be stored in storage.