Allow author to have no affiliation

lib/whedon.rb

@@ -85,8 +85,12 @@ def parse_authors(yaml)
 
       # Loop through the authors block and build up the affiliation
       authors_yaml.each do |author|
-        affiliation_index = author['affiliation']
-        returned << Author.new(author['name'], author['orcid'], affiliation_index, affiliations)
+        if author.has_key? 'affiliation'
+          returned << Author.new(author['name'], author['orcid'], affiliation_index, affiliations)
+        else
+          affiliation_index = author['affiliation']
+          returned << Author.new(author['name'], author['orcid'], nil, affiliations)
+        end
       end
 
       returned

lib/whedon/author.rb

@@ -18,7 +18,7 @@ def build_affiliation_string(index, affiliations_yaml)
       # to parse each one and build the affiliation string.
       author_affiliations = []
 
-      return nil if index.nil? # Some authors don't have an affiliation
+      return '' if index.nil? # Some authors don't have an affiliation
 
       affiliations = if index.to_s.include?(',')
         index.split(',').map { |a| a.strip }