Object is possibly 'undefined' when apply for number

I'm trying to make custom view component base on device size, but typescript complain about number, it said Object is possibly 'undefined', here is the code

export interface ViewContainerProps {  style?: ViewStyle | ViewStyle[];  children?: React.ReactNode;  percentWidth?: number;  percentHeight?: number;}export const ViewContainer = (props: ViewContainerProps) => {  const {style, children, percentHeight,percentWidth} = props;  return (<View style={[style, {height: onePercentHeight * percentHeight}]}> // no, this number is undefined!?      {children}</View>  );};

What happen, how to fix this, thank you guys a lots