Performance Appraisal - Need to get rid of "No Value" in drop down

Hello

In our appraisal document, the quality rating has been defined as a drop down box and I have defined 3 values for the same - "Low", "Medium" and "High". For some reason, the drop down is also populated with "No Value" as a possible option.

How can we prevent that? Also, we need to default the value "Low" for all the objectives. How to achieve that? Currently all dropdowns default to High.

Thanks