2893: Merge branch 'master' into 2893-no-symbols-in-db

Conflicts:
	services/api/test/fixtures/links.yml

diff --cc services/api/app/models/arvados_model.rb
Simple merge

diff --cc services/api/test/fixtures/links.yml
index b58f7c6e5c8aa048dea5b68e85caeb861de85b3f,fe77407fad1f76eda4c0c568f2338785e9448817..1fb1608f4de7b69ce881cb10c2a187edb90c4008
--- 1/services/api/test/fixtures/links.yml
--- 2/services/api/test/fixtures/links.yml
+++ b/services/api/test/fixtures/links.yml
@@@ -404,25 -404,16 +404,39 @@@ multilevel_collection_1_readable_by_act
    head_uuid: 1fd08fc162a5c6413070a8bd0bffc818+150
    properties: {}
  
 +has_symbol_keys_in_database_somehow:
 +  uuid: zzzzz-o0j2j-enl1wg58310loc6
 +  owner_uuid: zzzzz-tpzed-000000000000000
 +  created_at: 2014-05-28 16:24:02.314722162 Z
 +  modified_by_client_uuid: 
 +  modified_by_user_uuid: zzzzz-tpzed-000000000000000
 +  modified_at: 2014-05-28 16:24:02.314484982 Z
 +  tail_uuid: ~
 +  link_class: test
 +  name: ~
 +  head_uuid: ~
 +  properties:
 +    :foo: "bar"
 +    baz:
 +      - waz
 +      - :waz
 +      - :waz
 +      - 1
 +      - ~
 +      - false
 +      - true
 +  updated_at: 2014-05-28 16:24:02.314296411 Z
++
+ bug2931_link_with_null_head_uuid:
+   uuid: zzzzz-o0j2j-uru66qok2wruasb
+   owner_uuid: zzzzz-tpzed-000000000000000
+   created_at: 2014-05-30 14:30:00.184389725 Z
+   modified_by_client_uuid: zzzzz-ozdt8-brczlopd8u8d0jr
+   modified_by_user_uuid: zzzzz-tpzed-000000000000000
+   modified_at: 2014-05-30 14:30:00.184019565 Z
+   updated_at: 2014-05-30 14:30:00.183829316 Z
+   link_class: permission
+   name: bug2931
+   tail_uuid: ~
+   head_uuid: ~
+   properties: {}