use .or to fix all sorts of @map.mappings bugs

app/models/map.rb

@@ -16,7 +16,8 @@ class Map < ApplicationRecord
   has_many :events, -> { includes :user }, as: :eventable, dependent: :destroy
 
   # This method associates the attribute ":image" with a file attachment
-  has_attached_file :screenshot, styles: {
+  has_attached_file :screenshot,
+    styles: {
       thumb: ['188x126#', :png]
       #:full => ['940x630#', :png]
     },
@@ -31,7 +32,7 @@ class Map < ApplicationRecord
   validates_attachment_content_type :screenshot, content_type: /\Aimage\/.*\Z/
 
   def mappings
-    topicmappings + synapsemappings
+    topicmappings.or(synapsemappings)
   end
 
   def mk_permission