Given a multi-select element like so:
If the user selects only one item from such a select-box, then params.someName holds a single value (let's say '12').
Now, if the user selects more than one item from that list, then params.someName holds a list of values (let's say '[12, 20, 45]' ).
This makes additional boilerplate code necessary in order to cope with both situations. Even if such code is in place, it's still error prone, as the contents of the params-Map are Strings which will cause something like the following to fail:
A better solution would be to always pass a list, even if there was only one value in it. With the above example in mind, the content of params.someName would then be '' in case only one item was selected.