Move column_names assignment inside returning_selections

[mirelon]

When running the import, I was getting error from deep inside this gem:

undefined method 'column_names' for nil (NoMethodError)

Something is probably wrong on more layers, but the fix on this place is simple and safe, because column_names are not needed if there are no selections.

[jkowens]

I agree with avoiding the column_names lookup when there are no selections, but I don’t think we should move the assignment inside the map. That repeats the same lookup for every selection and makes the method harder to read.

Could we instead build selections first, then handle missing model metadata explicitly? For example:

column_names = Array(options[:model]&.column_names)

selections += Array(options[:primary_key]) if options[:primary_key].present?
selections += Array(options[:returning]) if options[:returning].present?
return selections if column_names.empty?