I ran into a little issue this morning with aggregation sum function.

I have some Notes that haven't yet the :attachments_file_size field persisted (the spirit of documents DB).
And when I run :

<%= debug Note.all.sum(:attachments_file_size) %>

it renders :

— !!null
...

As a workaround, I have to modifiy the lib/mongoid/javascript/functions.yml to take account of uninitialized field access.
I did the max & min function too (if the prev is 'start' and the field is uninitialized, it lets 'start')

max:
  "function(obj, prev) {
     if (obj.[field] && prev.max == 'start') {
       prev.max = obj.[field];
     }
     if (obj.[field] && prev.max < obj.[field]) {
       prev.max = obj.[field];
     }
   }"

min:
  "function(obj, prev) {
     if (obj.[field] && prev.min == 'start') {
       prev.min = obj.[field];
     }
     if (obj.[field] && prev.min > obj.[field]) {
       prev.min = obj.[field];
     }
   }"

sum:
  "function(obj, prev) {
     if (prev.sum == 'start') {
       prev.sum = 0;
     }
     if (obj.[field]) {
       prev.sum += obj.[field];
     }
  }"

Note: that doesn't break avg because the nil fields are already counted and (6 + nil ) / 2 is expected to be 3.

Can we have this for 2.3.3 ? I would be nice as it is a quick fix.