Fix for error when trying to parse a "publications" key with no value

This patches the broken site build caused by a new file in _research that contained
a "publications" key with no value. Rather than remove that line, let's make the
code a bit more robust so it doesn't break in this scenario.

Author: bsweger

_plugins/research.rb

@@ -29,7 +29,7 @@ def generate(site)
             end
           end
         }
-        if fm.key? 'publications'
+        if fm.key? 'publications' && !fm['publications'].nil? && !fm['publications'].empty?
           # Create hash url for publication page
           data['publications'] = fm['publications'].split(',').map { |kw| kw.downcase.strip }
           data['publications'] = 'keywords=' + data['publications'].join(',')