Power Query does not have an IFERROR function. It does however have another function that performs the same type of calculation.
It is considered best practice to use Measures for all your values in Power BI reports and dashboards. One way to make it easier to find Measures is to group them together.
Promoting headers in Power Query means using the first row as column headers. In Power Query this is a useful and common option. In some cases it is even automated. There is one time though when you don’t want to use it.