Hello,

[This behavior appears in a previous and the following org versions:
Org-mode version 8.2.6 (8.2.6-14-g063c8b-elpa @
/home/kosta/.emacs.d/elpa/org-20140505/)]

I recently began seeing weird behavior when trying to run `org-mobile-push'
in an agenda buffer; It appears the files are indeed pushed, but at the end
I get an error: "(wrong-type-argument arrayp nil)"

This only happens when I attempt to push from an agenda buffer - if I push
in a regular org buffer, everything works.

The stack trace is:
org-agenda-filter-apply(nil category)
org-agenda-redo()
org-mobile-push()

where the `org-agenda-filter-apply' call is from this sexp in
`org-agenda-redo':
(and (or cat-filter cat-preset) (org-agenda-filter-apply cat-filter
'category))

And cat-filter, cat-preset are set in a let* form higher up in
org-agenda-redo as (their values are included):

(cat-filter org-agenda-category-filter)
nil
(cat-preset (get 'org-agenda-category-filter :preset-filter))
("+Academic")

When I start emacs or even look at the agenda,
(get 'org-agenda-category-filter :preset-filter) always evaluates to nil
(up to the point where I eval `org-mobile-push'). It gets set in
`org-mobile-create-sumo-agenda', which is called at some point from
`org-mobile-push' before `org-agenda-redo'.

Apparently this started happening after I added the following custom agenda
command:

("z" "All academic agenda items" alltodo ""
 ((org-agenda-overriding-header "Academic todos.")
  (org-agenda-category-filter-preset
   (quote
("+Academic")))
(org-agenda-todo-list-sublevels nil)))

Now, I have two questions/comments:
1. It appears that `org-agenda-filter-apply' expects an array, and an array
always evaluates to togical t (As far as I remember, have just checked). If
this is the case, in the following sexp (from `org-agenda-filter-apply'):
(and (or cat-filter cat-preset) (org-agenda-filter-apply cat-filter
'category)) why is the (or cat-filter cat-preset)? It seems that either
`cat-filter' is an array, in which case it is (possibly) valid to pass it
to `org-agenda-filter-apply', or is nil, in which case it isn't. What role
does cat-preset play here?
2. It appears to me that `org-mobile-create-sumo-agenda' does not work
entirely correctly, as it leaves some properties set that were not set
before it ran?

Ok, so after writing the last two questions, I looked into
`org-agenda-filter-apply', and it appears that it expects a list of strings
of the form "+cat" or "-cat", which is what `cat-preset' holds at this
point.

Changing
(and (or cat-filter cat-preset) (org-agenda-filter-apply cat-filter
'category))
to
(and (or cat-filter cat-preset) (org-agenda-filter-apply (or cat-filter
cat-preset) 'category))
as a check and reevaling the defun makes org-mobile-push complete with no
errors even when ran from an agenda buffer. Note however:
1. There are several more similar lines in org-agenda-redo, which I suspect
also need to be checked.
2. After org-mobile-push, a category filter is applied to the agenda buffer
("+Academic"), despite the original agenda buffer having no such filter, so
it seems that something is broken in `org-mobile-create-sumo-agenda'
regardless.

I found a (somewhat) relevant post here:
http://thread.gmane.org/gmane.emacs.orgmode/57481
If what I wrote makes sense, let me know and I will submit a patch for
`org-agenda-filter-apply', and if I figure out how to fix
`org-mobile-create-sumo-agenda', for that as well.

Thanks,
Kosta