Treat blank UUID values as nil

activerecord/CHANGELOG.md

+*   Treat blank UUID values as `nil`.
+
+    Example:
+
+        Sample.new(uuid_field: '') #=> <Sample id: nil, uuid_field: nil>
+
+    *Dmitry Lavrov*
+
 *   Enable support for materialized views on PostgreSQL >= 9.3.
 
     *Dave Lee*

activerecord/lib/active_record/connection_adapters/postgresql/oid.rb

@@ -330,6 +330,13 @@ def accessor
           end
         end
 
+        class Uuid < Type
+          def type; :uuid end
+          def type_cast(value)
+            value.presence
+          end
+        end
+
         class TypeMap
           def initialize
             @mapping = {}
@@ -418,10 +425,10 @@ def self.registered_type?(name)
         register_type 'json', OID::Json.new
         register_type 'cidr', OID::Cidr.new
         register_type 'inet', OID::Inet.new
+        register_type 'uuid', OID::Uuid.new
         register_type 'xml', SpecializedString.new(:xml)
         register_type 'tsvector', SpecializedString.new(:tsvector)
         register_type 'macaddr', SpecializedString.new(:macaddr)
-        register_type 'uuid', SpecializedString.new(:uuid)
         register_type 'citext', SpecializedString.new(:citext)
         register_type 'ltree', SpecializedString.new(:ltree)
 

activerecord/test/cases/adapters/postgresql/uuid_test.rb

@@ -50,6 +50,11 @@ def test_data_type_of_uuid_types
     assert_not column.array
   end
 
+  def test_treat_blank_uuid_as_nil
+    UUIDType.create! guid: ''
+    assert_equal(nil, UUIDType.last.guid)
+  end
+
   def test_uuid_formats
     ["A0EEBC99-9C0B-4EF8-BB6D-6BB9BD380A11",
      "{a0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11}",