Empty cell value

[m-ovs]

If column contain some empty values the sorting fails with error "Column name "%s" does not exist in collection".
The error appears if an empty cell located in the first position in the table. So, if the empty cell initially not at the first position the ASC sorting passes well, but then empty cell took the first position and second DESC sorting fails with an error above.
For now I solved the problem just commenting this: /*return this._formatError(n[t],"sort",'Column name "%s" does not exist in collection',t),*/
But this is an ugly hack. Sorry, I'm not a pro in JS to make you a good PR.