Move non-existant keys to the end of the list when sorting. This is more intuitive as you typically don't want none at the top.

Author: tgmaxson

ase/db/table.py

@@ -96,7 +96,8 @@ def select(self, query, columns, sort, limit):
             n = columns.index(sort.lstrip('-'))
 
             def key(row):
-                return row.values[n]
+                x = row.values[n]
+                return (x is None, x)
 
             self.rows = sorted(self.rows, key=key, reverse=reverse)