Incorrect warnings when ckan.views.default_views is (almost) empty

[torfsen]

Due to #3011 I recently set

ckan.views.default_views =

in my INI, so that by default no views are created at all.

Since then I'm getting many warnings of the form

2016-06-06 16:23:03,537 WARNI [ckan.lib.datapreview] Plugin for view  could not be found

The problem seems to be that ckan.lib.datapreview.get_default_view_plugins splits the configuration value in a rather naive way:

default_view_types = config.get('ckan.views.default_views').split(' ')

Using .split(' ') will split on a single space, thereby creating problems with leading, trailing, and multiple spaces:

>>> ' foo  bar  '.split(' ')
['', 'foo', '', 'bar', '', '']

Even worse:

>>> ''.split(' ')
['']

To simply split on whitespace (as was probably intended), use the no-argument form of split:

>>> ' foo  bar  '.split()
['foo', 'bar']
>>> ''.split()
[]

Using split() instead of split(' ') fixes the issue for me. I'll create a PR.

A quick grep turns up a few other places with similar code (although I didn't check whether they are also problematic):

$ grep -r "split(' ')" --include "*.py" ckan ckanext/
ckan/logic/action/get.py:            fq = ' '.join(p for p in fq.split(' ')
ckan/lib/helpers.py:                                   kwargs.get('action', '')).split(' ')
ckan/lib/datapreview.py:        default_view_types = config.get('ckan.views.default_views').split(' ')
ckan/ckan_nose_plugin.py:##        #    testname = testname.split(' ')[1]

$ grep -r 'split(" ")' --include "*.py" ckan ckanext/
ckan/lib/base.py:                in config['ckan.cors.origin_whitelist'].split(" "):