
function _requireYieldSource(IYieldSource _yieldSource) internal view {
  require(address(_yieldSource) != address(0), "SwappableYieldSource/yieldSource-not-zero-address");
  (, bytes memory depositTokenAddressData) = address(_yieldSource).staticcall(abi.encode(_yieldSource.depositToken.selector));
  bool isInvalidYieldSource;
  if (depositTokenAddressData.length > 0) {
    (address depositTokenAddress) = abi.decode(depositTokenAddressData, (address));
    isInvalidYieldSource = depositTokenAddress != address(0);
  }
  require(isInvalidYieldSource, "SwappableYieldSource/invalid-yield-source");
}
