Error CS0161 'Purchase Invoice.Validation Datagridview()': not all code paths return a value code example

Example: Error CS0161 'Purchase Invoice.Validation Datagridview()': not all code paths return a value

public static bool isTwenty(int num)
{
    for(int j = 1; j <= 20; j++)
    {
        if(num % j != 0)
        {
            return false;
        }
        else if(num % j == 0 && num == 20)
        {
            return true;
        }
    }
    return false;  //This is your missing statement
}